The sound quality and audio level from the driven AF output of the transceiver is more then adequate and for general purposes the audio is quite good. Because this boat anchor speaker does not have the passive audio filtering which most external speakers have, it is often overlooked. I have hooked it up to a Radio Shack DSP-40 audio filter and this brings the speaker up to speed and makes an improvement.
If you are in the market for an external speaker, maybe you should look for one on eBay as quite frankly these speakers are a steal at US$35.00 approximately for final bidding price these days. What more could you ask for, and to boot a phone patching unit is built in.
With an external audio filter it would make a very nice unit for any transceiver, not necessarily the FT-901DM, FT-902 or the FT-101Z which it is intended to match. Cosmetically it is also an attractive unit.
This is oldie but goodie that is neglected today, some photos below: