I have had the iso's with the throttle boss for a couple of years, no problem very comfortable.

one thing that I did do at install that might have prevented some of the thottle tab breakage mentioned previously - it seemed that the iso sleeve was too loose, so I wraped some .020 inch thick plastic shim stock around the bar to make the fit better (once around, no overlap), this removes the side load on the throttle flange and tabs. pretty easy to do and cheap. the thickness of material might vary slightly at application.

05 speedmaster - 1100cc, 11:1 racing pistons, Carillo rods, thunderbike cams, ported and polished head, 2mm over intake and exhaust valves, Barnett kevlar clutch, scepter pipes, oversize manifolds, 45mm HSR's, TTP stage 4 firestarter