I ordered the flyin miata frame rail when they had a group buy so it was about $15 less than normal. I installed them and I will say that installation is a 2 person job. Someone needs to be under the car drilling a hole through the floor. The person on top needs to be able to attach a wrench to help tighten the frame rails to the car.
Now to the review. After I installed them the car did feel noticeably stiffer. They did not make the car handle better per say but they did decrease some slop in the suspension, and now the suspension works as it should.
I will say the most noticeable difference was over bumps. I noticed this one particular bump that was severe enough to make my cd player momentarily pause for a second and then continue playing. With the installation of the frame rails that has stopped.
This is not necessarily for its intended purpose but the stainless steel frame rails make a fantastic place to jack the car from. I don't worry about bending the pinch welds on the side. i just jack the car from the middle (around where the side mirrors are) on the frame rails and lift a side at a time.
I would rate the install was not that pretty ok if you are comfortable drilling in your own car. The enhancement that the rails gave was very nice and I would do it again.
PS. Make sure to coat all the holes you drill so that they do not rust.