I've been told they're not great but others tell me they are amazing, but for £200, a Marshall head and cab seems a bargain? What do you think?
Precursor to the MG?

No thanks.

1977 Burny FLG70
2004 EBMM JP6
2016 SE Holcolmb
They are solid state and for 200, I think thats about average for them.
If you want tube tone, go for a tube marshall, jcm 800
Personally, not my taste of amp.
I'm selling a tube Marshall combo for £200 which would be much better... Pm me for info
For £200 you probably shouldn't be looking at a half stack, it's not gonna be much good. Having said that, the MOSFET is much nicer than the equivilent replacement MG (In my experience)
Tbh I don't listen to all that much prog and/or folk :P My bandmates and I made a prog/folk band as a sort of side project/mess around so we had an excuse to use my mate's electric ukelele and my mandolin and stuff. For the record, these are the same guys I'm in a noisy/scuzzy/fuzzy/noisy/horrible 4 piece band with.