I've never played through one, but in a metalcore band with a loud drummer, at 300 watts, there's the possibility that it might not have enough power. The head only appears to work at 4 ohms, so that means (somebody correct me if I'm wrong) that you can't add another cabinet easily.
If you like the GK stuff, what about their MB500 head? They run around $500, and then you could get a a 4x10 cabinet, and you'd have more flexibility, AND more power:
http://bass-guitars.musiciansfriend....net?sku=486511
All for only $50 more than what you originally looking at.