I got a similar one on my blaster from ebay but its selectable from 2-4 stroke and its an hr meter and tach.Dont know how accurate it is but it seems pretty close.i use it for the hr meter more than anything but the tachs nice too.
Do a google search they make some pretty trick little tachs for the 2 strokes but theyre pricey the el cheapo ebay one i have is just fine.
Look into the single cylinder 2 stroke shifter karts and stuff like that for the good tachs.
Thats the one i have it works fine and reads alot quicker than that one.I also stripped the wire bare coming from the tach wrapped it multiple times around the plug wire on my blaster and used heat shrink to secure it not electrical tape.