It looks like a nice, no frills app, and to be fair there’s no pay to play gouging, and it just lets you play. Unfortunately it has two fatal flaws:
1) The random number generation is ridiculous. Not even close to being the averages of what you would expect from physical dice. Given how simple it is to generate a random dice roll in programming, I can only assume it’s by design and intentionally skewed for some reason. (Not even just the re-rolled dice coming up the same a ridiculous amount as others have mentioned, just bad across the board).
2) More than half the time (guesstimating) you don’t get two extra rolls, you only get one.
If they offered power-ups you could buy, or other IAP, I would say that they intentionally try to damage your score for financial reasons. But being they don’t have IAP or any other financial incentives, I can only guess it is just bad programming.