I assume you are referring to something along the lines of a PSS dripless seal. I made the change right after purchasing our 340 3 seasons ago and have had no issues whatsoever. Obviously, the boat needs to be out of the water, and the install is fairly straightforward and simple. I would recommend the PSS to anyone looking to get away from traditional packing.
You will no doubt get a wide variety of opinions regarding shaft seals from the group, but from what I've seen it really boils down to user preference.