It's worth it if you think it is, only you can answer that. Each class takes 1.5 - 2 hours to play through (perhaps less when experienced), and there are 5 classes.
If you're not sure what class you're going to start with on release then it's a good way of finding that out.
I think the most recent invites are more for server/queue testing than bug testing, since it seems to have been playing very smoothly to me this patch and I can't find any bugs or glitches at all.