Just got back from my first ride with the new Two Brothers Racing V.A.L.E.™ M-7 Carbon Slip-on and couldn't be happier with it. Fit and finish is top notch, and Two Brothers makes arguably the best looking exhaust systems on the market... the Carbon Canister version we installed looks awesome on our all black 2009 model WR250X. Sound is really really really good... a deeper exhaust note than a lot of the others we've tried (FMF Q4, Delta Barrel 4). This slip-on is designed to work with the stock WR250R/X header, but we got it to fit our Delta header without any issues. It would not, however, fit the FMF PowerBomb header we tried.
I will post a YouTube sound clip in a few days.
Notes: We also have an FMF EFI Programmer installed, as well as a 12oClockLabs EXUP emulator.