BBR
I have one.
Yes, it is loud (I ride a YZ400, the TTR is my girlfriends)
Yes it does boost power a bunch.
Spark arrestor is included. they also now have a small reducer (removeable) for low end power but it changes the exhaust note a bit. Not as deep, more restricted...
Also, make sure you open up the airbox, and the filter cage so it can breath better all the way through.
mike.
check out
www.ttr125L.com for more details.