You get what you pay for. If you're a seasoned pro who doesn't need a great deal of support, then 100% brokerages are going to be for you. I don't think these are necessarily the right places for new agents, though.
Considering my time spent reviewing contracts, time for me (or my assistant) to deal with filing/organizing, E&O insurance, and other miscellaneous costs, it costs about $350 a transaction just to break even...And that's running an entirely virtual operation. (Hence, I'm super picky about whom I would hire.)
You therefore need to have an army of hundreds upon hundreds of agents--all of whom are regularly producing--if you're going to be able to offer anything above the bare minimum support to them.