This was debated years ago by the SMAC and we voted against anything except oem tops. reasons:
They are still available new from Mazda. Expensive but available
They are still fairly findable on the used market. Been $1000 +/- for many years now
Most aftermarket tops are lighter than oem. Thus an advantage
Most aftermaket tops do not work with factory glass. Only bolt in plastic windows.
The NC aftermarket top was allowed in T4 for the following reasons:
Virtually unavailable on the used market as it was not a popular option
$2300 for new from Mazda
Aftermarket top acceptable in SCCA Pro World Challenge. With an additional 20 pound weight penalty over oem top. T4 has the same weight penalty.
Aftermarket top available from Mazda for $900 IIRC
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