So I was recently replacing a radiator on my 97 Miata. When I took off my drivers side fan my rusty POS decided to rip off the crank sensor and mess up the mount. I have been told that it is only used to detect misfires? Is this true and does this mean it is useless since I am running an aftermarket ecu?(speedy efi)

 

If I had a NA with provisions for an actual crank trigger wheel I'd be trying to fit an actual crank position sensor to it because it's a heck of a lot more accurate than the slapping timing belt.

Otherwise you are correct. The cam/crank sensor combo does all the fuel and ignition stuff and will work fine without the actual crank trigger.