I bought my current bike (Gravity 27Five G2) on bikesdirect. For the most part, I have been satisfied. The one thing I will say to keep in mind is that IF something does go wrong (such as in my case), you will be doing a lot of waiting for replacements to be shipped in.
I managed to get a defective front tire right away. I told them about it and sent pictures and they mailed it out pretty quick. The problem, however, is they somehow sent me ANOTHER defective front tire. After showing them again, they did end up sending me a new front tire.
My point is, if something does go wrong, it can be a bit of a pain when you can’t talk face to face with someone. That said, for the price, they are hard to beat. Trek, in my experience, are way over priced simply because of the name. Should you decide you want something else, you also have to go through the process of sending it back, which will be expensive. Just things to think about.