Not convinced by Blackstar's tones. They are too tight for my liking, not organic enough. I know, horrible cliché...
The ISF control is a posh way of saying a contour knob.
Many people swear by them, including Neal Schon, so it's probably me, but I don't get along with them.
For reference, the amps I've owned or own that I really love :
Marshall Jubilee
Marshall 2203
Peavey 5150
Laney GH100