it dont hurt ur car at all, Matter fact its better for ur car as long as u mate it with a good catback unlike slp or something that has no backpresure! If u can get away with no cats, Do it!!!
Why does slp have no back pressure?
Catless is better for power regardless what catback you're running. Some combos will sound terrible together, but a catless midpipe will make more power than a catted one.
The provide much less backpressure do to the muffler design, but thats a good thing.