The ones I had installed were the powerflex bushing inserts. I was not satisfied with the way the felt at all. Now, being that these are solid, the only concern that I would have is that they are a 2 piece bushing with a one piece cylinder in the center. I would still be concerned with that separation between the top and bottom piece would make me a bit uncomfortable.
If I was you and this is just my opinion, I would do it right the first time and install the M3 bushings. The stoutness and solid feel of the M3 bushes are well worth the money and really transforms the the rear end.
One last thing, if you don't plan to track the car on a occaisonal basis, I would not do the poly bushings. They are very rigid.
Quote from Ezeedee regarding car mods:
"you're only done when you sell the car