Thanks for the feedback! I will take some notes on these things as we continue with the beta and get feedback from all users.
Did you know that you can view your entire picks history under your account tab? A unique identifier could be included there without much trouble.
We use some technology on the picks list to filter out loans in which you have already invested, so that's why when you "Go" it disappears from that page; I want to ensure that you don't get billed twice for something you already paid for. If you were somehow unable to use the link, you can "Go" again for free on your account history page.
My primary goal is to keep things simple and powerful for the user. There's not much reason to worry about the sub-grade or even the actual interest rate, because if two loans are on the picks list, they are expected to perform roughly the same. If one is a D4 it probably has a little more risk than a D1, so that if you owned hundreds of each kind, the returns would be expected to be equal across both sub-grades.
Similarly, because loan purpose is already in the model, there's not much reason to stress further over it, either. The very rare small business loan that's on the list is expected to perform about the same as any other pick. When I need to buy into 50 loans, I just buy every pick on the list (with some very rare exceptions).