ive got a homemade solid fron one on mine with standard gearbox and rear mounts and its only slightly noisier/buzzier and not in a way i notice over about 2krpm- i noticed a huge difference in shift feel and spped and a general improvement in how tight and together the front of the car felt but having said that my old front mount was utterly shot to the point of no point having it so if yours is ok you'll be having less problems to start with.
im going to make a much harder rear one soon with only a capri/transit leafspringbush for cushion as the engine still leans back a lot when i sneak on the dyno at work and im worried about some of the top secret stuff im making hitting the bulkhead but thats another story.
bottom line, go for it, there seems to be no rhyme or reason as to rattles etc- i think some people are just luckier than others, they arent that dear and if it pisses you off you can sell it for most of your money back and certainly enough for a standard one
