although I think that there is written enough I'd also say, get one. if you are touring get the rack version, add wireless and a custom made 1u panel with the connections on the front side. you can than leave the rack closed on its backside (where it's often dark on stage) and have the rack standing upright. believe me, it's sometimes hard to find a suitable place for the poor, vulnerable, naked toaster.
powered or not ... if you can afford the powered version and often play live through a cab, get that.
Btw. my former equipment contained a 13u rack with two custom build preamps, tube poweramp, multifx, rackwah and more. I loved it but hated the weight. the kpa can replace this all (i use the non powered toaster and iem) but - to be honest: sometimes it's real fun to play the way we used to do (i still find myself sometimes carrying a tube amp head and cab somewhere just for personal pleasure :-)).
And I forget, I also had the super duper modeller with the best algorithms in the universe (including parallel universe, it's parallel universes and those universes in between) sometimes mentioned elsewhere, really tried to like it but could not...