Wont perform great any longer?
Different exhausts have a different torque/power curve, even if they might add power at certain
revs (that a stock scooter maybe can't even reach).
What are the chances that the new one you buy will have a curve that fits perfectly in the rev range
you have your scooter's CVT setup for at the moment? 0%.
Most performance exhausts actually have LOWER power and torque figures in the mid-range and then
a bit extra at the top, and you gotta tune your CVT to reach that.
If you buy a no-name brand / some random exhausts, chances are you won't get a dyno measurement
sheet with it and will have no way of knowing where that power increase is happening.
9 out of 10 times you'll end up with a louder and slower scooter.