I usually use a Bose L1, single sub, to monitor the Kemper onstage.
We recently did a gig in a venue with a famously small stage, and I used the power amp section of a Crate Powerblock, and the matching 1-12" Celestion GK-100 cab. 150 watts, mono Class D. I tilted it up toward me, like a floor monitor.
I used Monitor Out, cabs off. After a little global EQ tweaking, it sounded really good with almost everything. The inherent diffusion of the open back cab gave it more lateral coverage than a sealed back cab would have. The normally "sealed back cab" profiles really benefitted from the openness of the sound.
If I was using strictly guitar amp sounds, I would be tempted to use it all the time. But, profiles that need plenty of transparent highs would need major tweaking - acoustic sims, JC120, and some synthy things. Any thought of normal guitar synth also requires more than a single 12.