Are they really more sustainable that these one-time -used lithium ones?
Not having to buy new ones is very convenient.
https://www.amazon.com/MXBatt-Rechargeable-Battery-Capacity-...
If they actually had the 1200mAh capacity they say they'd have 1.8Wh which is much higher than a straight lithium-ion cell without the charging and voltage regulation circuitry taking up space.
Though even at their promised capacity, that's barely better than a normal rechargeable AAA.
And at the time there weren't good rechargable options. If modern NiMH had existed a few years earlier, lasting just as long as alkaline for a dollar each, they would have been the normal power source for those hungry devices.
IIRC, no indicator of charge, just had to guess based on the contrast setting. I think it did eventually fail to hold a charge, but it lasted several years, at least. Not as good as NiMH from several years later though, but it was better than buying batteries all the time.
I see discarded disposable vapes multiple time a day every day, I don't remember the last time I saw a battery.