does anybody have experience with these mufflers?

a quick youtube search pulled up only a few lt1's with these mufflers. to be honest, they dont sound that bad for only $29.99

I have not heard of anyone using a thrush. It may sound good, but will it perform like the higher end mufflers and cat back systems?

I also have never heard of them. I would stick to a well-known brand, because then you are guaranteed quality as well as proper fitment. Just my .02

A friend of mine used some type of thrush mufflers on his truck. Fairly quiet, though I can't remember what type of thrush the were. I'd go ahead and use them if you have a small budget. At the worst...you spent $30 for first hand experience of why you get high end mufflers lol.