I like them. I have them on my 80's sears mowers and only ever needed to change oil and add gas.
Borrow a cyl compression test tool from car parts store and test it before u buy it.
If it has the charging wire, test that it puts out 14/15ishVolts.
Listen for any loud rattling noises and it not leak oil.
Lastly, what are you using it on? Mine are on 38" mowers. If yours is larger cut, u likely need more HP.