Last night I used GP to run FoH for a (very very small) event and it worked a treat.
Due to various issues we had to jury-rig a PA from a powered speaker, a FocusRite interface and my laptop for 3 inputs plus some ambient music.
I would say it took me about 5 minutes (no pre-planning) to create a rackspace with gain control, EQ, and compressor for each channel, plus a parallel reverb with send level for each channel. All of this added and widgeted very quickly and worked first time. Then just controlled the mix using fader widgets and opening the plugins as required (with more time I would have widgeted those as well).
‘Next time’ would bring a MIDI controller as mixing with a mouse isn’t much fun, but all worked perfectly and this would have been a right faff using Mainstage!
Keen to develop the gig file a bit more and use it with a higher input gig - more than happy to use this rather than a ‘real’ mixer if the situation required.