Not an Olympus user, but I've used the alternatives with many other cameras & meters.

Very satisfactory, just as accurate as the original meter, life varies depending on the alternative used.

My favorite is a C.R.I.S.-type adapter with silver cells. Wein cells are expensive and have a relatively short life, though some people report that by partially blocking the air hole, life can reach a year or so.
Hearing aid batteries can be cheap and in many cases simply a wadded-up ball of alu foil is all that's needed to make them fit.

Pay no attention to some nay-sayers who call these solutions "fiddly" and improvisational: I haven't once regretted using them or missed mercury cells.