I've run these in my racer - they're good if you remove your engine on occasion for refreshes / etc.
I secured the mounts to the engine and to the body, then just 'pull the pin' to disconnect the two (first removing the two safety clips). Much quicker and neater than rubber mounts.
Done plenty of races with it. No the pin hasn't snapped off

The mounts are made from polyurethane so they don't flex much - the pin is mainly to locate them snuggly.
Didn't notice much extra vibration, my car body is pretty stuff (rollcage / hard suspension). Would probably get away with it in a road car.
I found them easier to fit than standard mounts because they are two-piece you just push weight on the engine to get it to sink further before you slide the pin in, or use a jack to adjust the height of engine/subframe.
Not like the old 'stick the screwdriver into the engine mount to force it to align, then slip the bolt in and tighten.
Incidently, I would stay away from captive nut engine mounts and welded nut engine mounts IMO - too hard to fit.
I've just finished refitting rubber mounts to my racer to compare the difference so i'll let you know... am taking it out this weekend. Will post up a HOW-TO replace engine mounts in a few days as well
Fit either standard rubber mounts or two-piece polys. Oh and i'd go for genuine rubber mounts if you don't have much patience
