They're fine if you're sticking close to what they intended for equipment. I've almost always had to re-swage the big cables though. I don't use them unless I just get one somewhere and use pieces, but I have a bunch of wiring stuff laying around.
When I bought one 6 years ago there was a lot of wire for less than it would cost to buy elsewhere. Unlikely that it will meet your needs in terms of system design unless you stay very close to their standard panel.
