I love my GT6-B. I've never sat down to compare between the effects and the pedals it's modeling, though. You can look through these threads and find at least one person who loves and one person who hates almost every pedal in existance. For me, the only question is, "Can I get a sound I like from it?" Maybe the unit might not make your bass sound exactly like it would through a Boss Chorus pedal, but I'd be stunned if you couldn't create a sound that you love with what they give you. The main weakness in the lower end multi-effects gear is a lack of paramaters you can tweak, but there's certainly no shortage here. I'll be exploring my GT6-B for years, and every new sound leads to seven new songs! If you can get one cheap, do it!
BTW, has anyone tried to combine this with an Aphex Aural Xciter? Just wondering what the results might be...