I have played in games where it was allowed, and we basically used 1 DP = 1 TP, but we also required a plausible explanation for the gaining of the talent (or the buying off of a flaw in some cases). It worked pretty well, as the GM did have veto power over the whole process, so the players did not always get what they wanted.
And in doing it in the manner you are doing it -- do you require them to spend their DPs right away? or do you allow them to save DPs up to get something? As long as they can save DPs that works fine.
And don't forget, as GM, you can also go in and change the costs so that they are more suited to your setting and campaign (i.e. increase the costs of the talents you want to be rare, remove from the list altogether those talents you don't want to allow at all, etc..).