I have one PLUS a fishfinder. Frankly, I've never bothered to locate the Seafarer's transducer...it must be directly under the nav station in the old boat.
So I've kept both operational. I find with certain bottoms, the fishfinder isn't quite happy to give a consistent depth, whereas the Seafarer will give, when the gain knob is tweaked, as accurate a measurement in chains or fathoms or drams of sheepfat as it is capable of giving. I enjoy its cathode-lit endurance...it's easily the most ancient working bit of electrical gear aboard.