I've made a decision. Despite the extra cost of the amplifier, and the outrageous cost of the foot pedal and/or expression pedals, I'm going to go for the Katana.
This additional vid helps to explain it a little more, perhaps.
Although it only has 4 patches as well as an and/or pedal chain, the effects are Boss pedals and tweakable via the PC/MAC app. The variable power output was a major plus for me too.
I will sell my V1 Mustang and keep the V2, which has stereo balanced outs for my (very occasional) live use, and obviously a completely different sound palette.
Just waiting for some funds to clear before tapping Thomann for a delivery.