Agree - save money for VAC/PRESS tester, but some may want a compression reading if you're selling the saw. The Schrader valve must be as close to the combustion chamber as possible, especially on small cc engines. Be cautious if using an adaptor, it can increase combustion chamber volume and reduce the compression reading. I just experienced this on an MS171 which uses a much smaller spark plug - the adaptor changed the compression from 130 to 90 psi. I modified the adaptor to keep the valve at the end.
btw, Amazon has a gauge made by Lisle that works well for about $27.