I guess that I will chime in here. I had an 08 MS3 with several different MM. Because of marriage to a woman that is unwilling to drive a stick, buying a house, and getting a job that was further away I bought an auto (only 4 ******* gears!) 04 MZ3 (which i regret every day)... that being said.
Buy the TRZ. It is proven on cars that would beat them up way more than our 2.0 or 2.3s will. I was running a Delrin TRZ in the rear, and custom tranny mount, and a TopSpeed passenger side.
DONT BUY THE DELRIN! It is way too harsh for anyone asking whether they should buy it or not. It is really stiff and you will probably hate it.... personally I loved it... but I'm crazy...
The tranny mount does cause a lot of whinning from the gears, but it changed the shifting feel and acceleration so much I personally think that its totally worth it. TRZ also makes one of those, but I havent used that one. The reason that I didnt go with that one was because it used the bottom half of the stock mount and I want a totally aftermarket mount. However, at this point people have been using them for a while and like them a lot (at least the MS3 drives that I know). Also, because the TRZ uses the bottom portion of the stock mount guys who are worried about installation should have a little bit easier time getting it in there.
Lastly, the driver's side mount. I can not find the Top Speed mount and it makes me cry a little. That was the best mount on my MS3. It was solid rubber instead of the liquid filled stock mount. It did not add much (if any) vibration, but did make the car feel more solid.
If anyone knows where I could buy a Top Speed passenger side mount for my 2004 MZ3 I would be in their debt! If you are interested in the doing mounts all the way around the car you could always get a torque dampener"(
http://www.protegegarage.com/1742-ingalls-stiffy-torque-damper-mazda3-mazdaspeed3.html) on the passenger side to round out the set up.
I hope that this has helped.