The Dark Drive is very crunchy. I like pairing it with the Bass Fuzz to get some really narly tones. I think Boss missed an opportunity not to include these xtra bass amps right the beginning. A common complaint I kept seeing is the lack of bass amps. I think the GX 100 is an excellent deal.
The Fat Tube and Solid Stack Amps are freaking amazing! I'm mostly using the Fat Tube mostly but when I want that GK sound I'd say Boss did a damn good job with their take on it.
I haven't used the Dark drive much since I haven't set a parallel chain yet but when I'm ready to go down that rabbit hole I know I'll get killer results.