For my 750 the balance pipe works best, Ive tried OEM type siamese, and Dunstall type 2 into 1 passing beneath the motor, and a few silencer styles, short mega, Dunstall type mega, Goldie style, I get best sealing, security and performance from the stock 71 set up, I have never tried the FS type, mostly because i like my skin uncooked..
The balance pipe I have currently is no worse a rust trap than all the tight bends in a FS set up.

71 Devimead, John Hill, John Holmes A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod