I would never use an external meter on any camera with a built in meter. The center-weighted meters on my OM's work great, as do the body mounted meters on the RF's. You should be aware enough of the light variation across the scene to adjust the exposure accordingly. The few times the spot metering on the OM-4 is used is mainly for curiosity and education.
In having used various hand-helds with my folders and other unmetered cameras, the results have alwasy been spotty. It is impossible to know exactly what the meter is "seeing", or if it is pointed in exactly the same place as the camera. I probable run about 50-75% correct exposure with a hand -held, vs 99.9999999% correct with an in camera.
Of course, if you are shooting print film it doesn't matter either way.