I don't have an underfolder AK but I have a side folder VZ58 (VZ2008). I don't find it uncomfortable to shoot but it certainly doesn't offer the same secure cheek weld as a carbine with a solid buttstock.
I really don't ever expect to do any urban fighting or house clearing myself
but the original design intent was to have a light, short handy CQB rifle that could also be used at longer ranges by simply folding out the stock.
I like how compact it is and in a worst case scenario police-state hostile environment situation, then having something concealable in a back pack for humping over the back trails out of town on my mountain bike is nice. Again, not something I expect to happen in my lifetime, but it's nice to have.