Whenever I read a post like this it makes me smile. I am a real cheapskate, and I have spent half my life buying the "next product down", hoping it will work satisfactory. Unfortunately, with very few exceptions, I have been utterly disappointed. I kept thinking, "maybe it is made in the same factory and just has another name stamped on it."
What I have found is this: Sometimes, if you pay 3/4 of the price, you'll get a decent product. But, if you pay less than 3/4 the price, it will not be satisfactory.
I'd say you'll be sorry in a few training sessions. IMHO, weapons mounted lights take a real beating. Let us know when you have a couple of hundred rounds downrange with it. Remember, you're going to have to test the setup to make sure your pistol still fires. It could be that the extra weight might make the gun malfuction, at least with lighter loads.