Sold hundreds of them here over more than a decade and never had a single manufacturing issue with the Fidanza product. Have checked the balance on them dozens of times and found them spot on... Thus, I have a scientific basis for my judgement, hundreds sold over more than a decade and never a single issue here with the product. Thus, my conclusion is actually rational...if there was any issues on these we have seen enough of them to uncover the problem yet never once had an issue here. When you guys have PERSONAL experience involving hundreds and hundreds of the same part number going back over more than a decade then you will have a logical basis for suggesting another conclusion to me. We did once have an issue on the cheapest F1 flywheel we sell for NA/NB when it was found they didn't tap the threads all the way through, but even that was just one example among many sold. In brief, a flywheel is big dumb spinning weight and pretty easy to make. Thus, issues with accuracy of the product have been very rare.
In contrast, forum gossip not based in reality or based instead on some experience with some other motor application is not relevant here and might easily be explained by some install mistakes on that other application. Reminds me of a guy at Miata.net trashing an IL MotorSports intake the other day and it turned out he bought it used and didn't know the history of what abuse it might have suffered and he did not have the torque specs and overtorqued the bolts on install and screwed up the product through total ignorance and incompetence....but he still blamed the product and was telling folks to stay away from it. Amazing...but typical that complaints about a product usually come down to install mistakes. I see folks screw up the flywheels and bearings by bashing them during install (hint....put the flywheel on hotplate or oven to heat it a bit and the expansion will let you complete assembly without any brute force whatsoever). And, though the less expensive versions always get more complaints I will suggest to you that our experience is that the real reason is that the customers buying the less expensive versions tend to be the customers doing the install at home and then blaming the product when their install abuse creates the problem. In contrast, the customers who buy the more expensive versions of an item tend to hire a professional to do the install and professional installs have a MUCH lower percentage of errors. And from this result the forum legend grows that the more expensive version is somehow 'more smooth'....
Note that you get less smoothness with any lighter flywheel because you need to give it more gas to get away from a stop. The less weight, the more gas you need to give it. And if the transmission is old, the result of adding any light flywheel will be less "SMOOTHNESS". The brand of flywheel has nothing to do with it. The flywheel is an amazing damper.....and the lighter you go, the less damping effect you get and the more rattle you get in an older trans. And the older the trans, the less smoothness you get. Thus, it is often said that adding a light flywheel will uncover or reveal the age in an older trans and adding any light flywheel can result in a complaint that the transmission has more rattle or less "Smoothness" than before.... but that's just a matter of simple physics, the brand has nothing to do with it. Yes, have had customers come back and had us switch the brand to the more expensive flywheels because they read in a forum about how it would be more smooth....and every time the result is the same as before with the cheaper unit....and the unit removed will test perfect.
Thinking out loud....I could imagine a Sports Car DMF (Dual Mass Flywheel) for the Miata. These are most often used on diesel motors and are amazingly effective at killing all vibrations and giving much more smoothness. But I could imagine a super light weight high tech version for Miata (the BMW M3 has a DMF). But so far, all the Miata flywheels I have ever seen are not DMF designs, even at two or three times the cost and Mazda's own history with DMF has not been good (high failure rates on Mazda6 diesel).