Based on an interesting post from My Personal Finance Blog discussing setting-up his individual 401ks.
I actually decided in the opposite direction: against going with 401kbrokers and instead going with Fidelity.
Although 401kbrokers does allow borrowing against a 401k account, I have a separate cash reserve, so that is not a significant requirement for me.
What is interesting is that I can invest in the various fidelity index funds, some spartan, mutual funds have expense ratios as lows as 0.08%. That sure beats whatever 401kbrokers offers, even if you can use Vanguard mutual funds - after all, they tack on 0.25% admnistrative fee.
Somehow I have a visceral dislike for any kind of aum based admninisrative fee.
Also, there's less institutional risk - Fidelity has been around alot longer than 401kbrokers.