I have an EZ Tach +PLUS (Model 328) from Electronic Specialties, it can be used wireless or with the included inductive lead.
I've never checked the accuracy against another tach... but, I don't get surprising, unexpected, or obviously questionable readings from it neither.
I use it mostly for setting up governors on 4-cycle OPE, but I have used on a few 2-cycle engines.
It don't have instantaneous readout though, it updates the display every second or so.
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