I don't see a problem with it, you are only allowed 8 per Season and 1 per Tour.
The sole reason the idea came about was for a little bit of protection against those odd shots that you fail because of lag or something, sure you can use them simply to try and improve a bad shot though.
You can't achieve 3xBull or Perfect Game by using them, you also can't use them in Sudden Death or Tiebreakers.
It is true though that Darts doesn't "need" Mulligans, but then again, nothing really needs anything...