The TTR is widely used, ‘cos they’re out there and they’re cheap(ish). The TTR header also has the advantage of being Stainless Steel, so is lighter than the TW counterpart. In theory, because the thickness is less, it will be more noisy, but no-ones complained yet. It’s also rumoured they polish up quite nicely too, though keeping it that way could present some difficulty
The diameter of the header pipe isn’t likely to make any difference to jetting, as at one end, it’s restricted by the hole in the cylinder head the gasses come out of, and at the other, by the speed at which that gas can escape, eg the muffler. What goes on in-between those two points is largely academic in the world of exhausts. You could delve into the world of “power bombs” et al, but on a TW, the issue of recoil is pointless
Anybody who’s trying to sell something will tell you what you want to hear, and other than the “smug grin”, mostly from the seller, it all becomes a placebo — stick with the TTR
Here’s your torque setting, be gentle, the bolts are old, the threads are dry and rusty, and getting a busted stud out of there is a complete pain …..