Nirvana pros:
Cheap, lol.
Mostly pretty solid stuff.
You will probably be able to find a nice mother in your 10-pack.

Nirvana cons:
Not the originals
Often F2 or even F3 generation stuff- there's going to be variation

It's up to you. Personally, the stuff I've bought from Nirvana has been lines that are already relatively stable- classics like Skunk 1 and NL- so it doesn't bother me. IF I were going to get some newer fancy strain, I'd check elsewhere as well and then weigh costs. I've been satisfied with Nirvana with the sole exception of their white rhino, which hermed on me while everything else in the garden was fine.