That is pretty much what I was asking. What do you typically use this type of rig for? AMBC and SW broadcast?
The BC-348 was AM and CW, but it works OK on SSb too. Mine just has a messed up non-working BFO. I traced it to the oscillator coil, and I put it aside.
By definition, a product detector is just a mixer. A diode detector is a product detector, once injected with BFO signal. We all know a diode makes a good mixer when injected at the correct level.
A human would be very hard pressed to hear any difference between a complex product detector with a double balanced mixer scheme and a simple single-diode mixer.
The real reason old radios suck for audio quality is they almost always have inadequate BFO injection levels, and they usually have poor AGC while the BFO is on and also for varying levels like SSB and CW.
My SX101 and NC303 have severe audio distortion on CW and SSB when the AGC is used but, like most old rigs, sound pretty good in manual AGC mode.