I installed the Cobra Speedster Slash Downs about 5 months ago and have ridden the scoot on many trips long and short. I am very pleased with the Cobras. Quality is good, not great, but good. Check the flange at the head for a weld seam as I have heard of many that this needs to be ground flat. Mine did. Use new gaskets, I tried reusing mine and it leaked and backfired very loudly.
The Cobras are loud, and compared to stock your first impression will be wow this may be too much. I can tell you when you need to be quiet the Cobras will go softly, but when you get on it they will bark and announce your presence. On long cruises they are very pleasant not too loud, I wear a shorty helmet and have no need for ear plugs. Most of my friends with HK and V&H wear ear plugs as a matter of course.
No jetting when you put on just the pipes. I did open my
PMS from a Stock 1 3/4 turns to about 2 1/2 turns and it ran great. I am at sea level. When I added the
BAK I rejetted to a 170
main, 4th groove, and 3 tuns on the PMS. I have opened the PMS anothe 1/4 turn as the weather has cooled. It runs great, gets good mileage and the sound is all I wanted.
Good luck