I have the TTI 3" X pipe under the trans tailshaft and ending at the rear end with regular Ultra Flo's on my race car. Works great, picked up over open headers and I've gotten a lot of compliments on the sound. I can hear my Holley fuel pump at idle, but it gets pretty loud at WOT.
I might go to the bullet-type eventually to save some weight and room.

I haven't tried the X-muffler but it just seems like too much going on in one spot to provide optimum results.
Seems like you might have to offset the muffler for optimum clearance. Can't see it directly under the driveline somewhere.