Tachometer for Chain Saw Tuning

My concern would be the size, it may be small enough that it flops around when you are trying to use it. I have an old Stihl that I used to use all the time it's the size of a calculator.

The wire around the spark plug would be an invconvenience, but probably worth it for the money and for occasional use.
I have a nice non-contact one. To be honest, I use it more to check spark when ppulling over an engine, or for L&G small engine work.
For saws, unless it is bone stock, with the same b&c as the manuals specifies, I find I end up tunign by ear anyway.
It is good to check after the fact, make sure not over revving, and I supoose writing down the number for thaty combination tyo come back to it later might be helpful.
It is helpful after a muffler mod to be very sure it is not overspeeding.