To be honest my Eleven Rack has only been plugged in once since I got the Kemper 4 yrs ago. I probably should give it ago as a backup.
I used it live for about 9 months without any issues at all. And while it is no Kemper I found the tones to be pretty acceptable and certainly more then adequate as a backup
I don't believe Avid has done an update in a couple of yrs
My experience was the opposite. I bought it, liked about 5 of the presets, found it difficult to work with (i.e. noise gate was on every patch but to turn it off was difficult, not global)
I ended up quite glad to sell it.
I guess you are looking for a cheap backup, but the FX ULTRA was a far better unit in every way. The tones were amazing compared to the 11R and the FX first class, so that you can even use it WITH your Kemper. Plus it has solid equity, so think of it as an investment where the "loss" when you ever sell it is the rent you pay for having used it.
My thinking is this: Why get a so-so unit for a "may never happen" scenario when you can have a solid unit that you can actively use in conjunction with your KPA now?
For live backup I'd consider a Pod Xt / HD500 floor unit.
It's a good sounding backup, very sturdy and will also function as a MIDI foot controller for the kemper.
I listened back to some recordings I did with the 11R and the tones were a bit brittle and plastic sounding. If you want a backup amp modeller that you can throw in your bag then just get a Sansamp character pedal like the Blonde or the Liverpool. Or even the Joyo American which I hear is just as good.
My experience was the opposite. I bought it, liked about 5 of the presets, found it difficult to work with (i.e. noise gate was on every patch but to turn it off was difficult, not global)
I ended up quite glad to sell it.
I guess you are looking for a cheap backup, but the FX ULTRA was a far better unit in every way. The tones were amazing compared to the 11R and the FX first class, so that you can even use it WITH your Kemper. Plus it has solid equity, so think of it as an investment where the "loss" when you ever sell it is the rent you pay for having used it.
My thinking is this: Why get a so-so unit for a "may never happen" scenario when you can have a solid unit that you can actively use in conjunction with your KPA now?
This makes a lot of sense - the whole rental thing is a good point.
Yes,it is all about a "cheap" backup for the live thing.
All the thoughts above are reasonable,legit and very welcomed.
The Ultra costs some 1000 euros here in europe so it is not within my "backup-budget".
The L6 stuff..hm..dont "like them" anymore for several reasons.Most of all I dont like tbe sound and they have a very bad custumers service when you try to get help or even some information on their older stuff.I still dont know what kind of speakers are installed in my old AXSYS-combo.And as far as I know I was not the only one who tried to find out..
I need more info about the 11R I guess.
I think the 11R has the same sonic fingerprint as the Line 6 stuff. It is a bit better than the POD but I felt the sansamp stuff was more organic sounding, lighter and cheaper.
The character series is pretty good. The old 'classic' is my fave for clean sounds but it doesn't take distortion well because of the headroom. But the newer ones like the Liverpool have more headroom. Great as a backup.
It is also worth bearing in mind that the 11R is basically the Eleven plug in in a hardware unit. If you can try out the plug in you can hear what 11R sounds like.
To me for backup solutions SPACE is an important factor, more so than money.
That's why I'd never bring another rack unit to the gig.
I'm using a Zoom MS-50G and if my Profiler ever failed this would get me through the gig.
To me for backup solutions SPACE is an important factor, more so than money.
Could not agree more dear Ingolf..
But for these kind of "very small gigs"(grab and go";) the question (at least for me) is not if I have a 3HE-rack or a 5-HE-rack but rather where to put any kind of rack next to the espresso machine on the bar at the entrance of the students-bar.. 
..ofcourse there is not even the space for the monitor..
This is because I had the "dream" of a floor-style Kemper "profile-player".Now..if I play the gigs with the KPA/Remote/FRFR-combo 3 or 5 HE are not my issue.It is more the bad experience I had with no back up at all.This happened twice to me.Including angry bandleaders and venue.owners.Dont want to start with the "murphies law" bla bla but to be honest I feel much better with some back up.
Could not agree more dear Ingolf..
But for these kind of "very small gigs"(grab and go";) the question (at least for me) is not if I have a 3HE-rack or a 5-HE-rack but rather where to put any kind of rack next to the espresso machine on the bar at the entrance of the students-bar..
This is because I had the "dream" of a floor-style Kemper "profile-player".Now..if I play the gigs with the KPA/Remote/FRFR-combo 3 or 5 HE are not my issue.It is more the bad experience I had with no back up at all.This happened twice to me.Including angry bandleaders and venue.owners.Dont want to start with the "murphies law" bla bla but to be honest I feel much better with some back up.
I hear you @Nikos but the ZOOM MS-50G @Ingolf is reffering to is a complete (FXs + amp tones) solution that will fit in your guitar gigbag pocket! Probably the lightest and smallest complete backup available! 
Exactly @Pick909, it's a complete backup solution and sounds decent.
I have an 11r as a backup and while it's not a Kemper it's pretty damn good. You can easily dial in some great tones with it. One thing it has that sets it aside from cheaper pods is the true-z input which gives it a real amp type of feel (I tried a pod hd and turned it off immediately). As mentioned, the noise gate was one of biggest pet peeves especially with a high gain sound, but for $300 ish you can't go wrong for a backup IMO. It's also pretty light for two rack spaces.
I guess I'm spoiled...here is my live rack (top) and stay at home studio rack (bottom). I've been grabbing the bottom rack and setting it up like this for live gigs "just in case". The studio rack can be plugged in to the remote and input in a couple seconds if I have a failure and is ready to go. The nice SKB 4 space rack is super lightweight and no problem bringing along to gigs.
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...and I also have an 11R in my studio that I never use. Tried using it live once and thought it sounded awful through the PA direct.
<p>A lot of the smaller venues in the UK won't let you use your own backline due to safety regs (they want to make sure anything running on their system is properly tested). Interestingly they don't care about floor FX units. So if they won't let you plug in your Kemper or similar rack unit because it looks too much like an Amp you could probably get away with a sansamp.</p>
