This question, I'm sure, has already been sufficiently answered; I will add this, though. There are a gazillion ways of using your TCredits, but one of the things that I have seen from TCredits is that they are very easy to come by.
If you buy the 125-pack, I suggest use 100 of them monthly for bidding in a 2X auction. If you do that, even if you lose, at least you would have made 1000 MRP for the auction. That's at least 1000 MRP monthly.