I would say it would be reliable if you know what one model feels like with a piston and cylinder in good shape as it goes down the rope.
I can feel a big difference on models that I have rebuilt and ones I pick up to do the rope fall test....
As others have said, pull the muffler and check the piston and cylinder from the exhaust side for the best indicator, next to a compression test.
Also, if you don't see scoring but the compression is low, the saw may have a lot of hours and the ring may be worn. Installing a new ring may be all that is required to get it back to healthy. Sometimes the piston will be worn and sloppy as well, but the cylinder will be fine. In this case, install a new piston and cylinder.