I got the Streamlight TLR-2 for my XD 40 Tactical. I wanted a light, but also wanted a laser for practice / training to improve my trigger pull. I assumed it made sense to get the combined laser + light model.
As for Streamlight, I think my reasoning at the time was that the reviews seemed good compared to the complaints about other brands (switch problems and battery cover complaints on others), and the price was less than most other models.
But I was surprised by how large it was when it arrived. It is moderately bulky, and makes my XD feel much heavier, totally changing how it feels in the hand and handles for things like a mag change.
However, I'm assuming that the weight perched at the end of the gun helps a bit with muzzle flip. Although I'm assuming you don't need any help with recoil on a 5.7.
And since I just keep it on the gun all of the time now (even at the range when I don't turn it on), I've pretty much adjusted to it and become used to the bulk and weight.
If you only want a laser, then I would probably recommend getting a dedicated laser instead of the laser+light combo. The light adds alot of bulk and weight.