If you're referring to my comment, Fidelity isn't as web-friendly as Vanguard, but they've been fine to work with on the phone.
The biggest drawback to Fidelity (for me) is the active management and fees that go with that, and the inability to pick specific funds (I put mine in the 70% equity option).
But for a minimal account balance, the higher management fees are not much of an issue either, far outweighed by the benefits of the credit card. And as TJ suggested, you could even drain down your account periodically if you wanted.
So go for it -- get it quick, while you can. I'm not sure how long the deal will last.