Hello! The Nippon is a Clairtone 7978 aka, a Rising 20 20 aka . Those are readily available most times in the $550 CDN +/- range depending on condition, accessories and functionality. Mint in box, possible $1k. The first Gen 931 is a Gem depending on it`s condition, and most importantly the band selector switch and the function switch are notorious for breaking. Plastic gear that if one has the ability, a precision metal gear can be had specifically for removing the switch from the board, taking apart the switch , inserting the new gear with great success.
The tonal quality of the 2 , i have both these are an opinion :
Clairtone , great with loudness on and low volume - maybe 3 1/2 - 4 .Bass follows nicely sounding like there is much more potential. After 5, loudness off , bass down a few notches and when turning to 8 , if the bass isn`t turned down the speakers distort. Small magnets on 8 inch woofers, a bit disappointing. When using external speakers same impedance, amplifier has no problem driving them. Punch key operation. Quite mechanical , and very reliable after servicing. Clairtone uses wider FBS belt for main drive.
Lasonic : Larger magnets on woofers, graphic EQ for tone control: The 931 handles the speakers well. Although known for less than adequate build quality (shell, transformer mounts that break easily in shipping) The electronics were impressive. Point to point soldering as opposed to plugs although they did use ribbon cables that pressed into a gang slot of 4 or more connections - The tone controls on the 931 are fantastic for low end pump, but the highs seem less than adequate and feels like there is a hollow spot in the sound. In most cases, finding a spot that is close to your expectations is good enough. Still a great unit overall with decent clarity depending on adjustments. Deck is similar in punch key operation. Deck belt configuration very simple thin basic sbs belts. Very similar to the recent Vela DK-9000 I serviced, in fact near identical. My Technidyne TD-7000 same. The slide in deck is a nice feature to have, reminiscent of the old car stereo days. Just restored one a few weeks ago and the clarity of the slide in deck wound up being cleaner sounding even after demagnetizing and cleaning and adjusting azimuth on the lower deck.
Bottom line? Get them both if you can. Every boombox has it`s own personality and these 2 make a great addition. If you can only get one or the other, that is up to you. Good luck!