I'd suggest he try the free Mac B5.5 at download.com. If he likes it and especially if he's running on an multi-core Intel Mac then consider getting 6.1. B5.5 runs under Rosette emulation as well as only using 1 core on a Intel Mac, which makes it very slow to render - 6.1 is Intel native code (Universal Binary) and has multi-core support.
If he's running on a PowerPC the main reason to upgrade to 6.1 is for the new features.
Another good reason to get 5.5 is that for the DAZ March Madness sale the 6.1 upgrade is something like 40$ (US).