From what I understand the NEMA 14-30 plug is not meant to be plugged and unplugged from the socket daily.
This is a TMC urban legend. I don't know where/how it started, but the NEMA plugs and sockets are certainly heavy-duty to be plugged/unplugged thousands if tens or hundreds of thousands of times. The 14-30 and 14-50 components are 100x beefier than your everyday 110v plugs and sockets used in everyday appliances. And how often do they fail?
Also, even if this was a real thing, if you have a UMC for charging in the garage, it usually just stays plugged into the NEMA socket, it's not plugged/unplugged daily.
If you have a garage and can leave your plug there from your UMC set, that might be fine, but I think it charges at a lower rate than the HPWC (single charger, @40 amps, 29 miles/hour charge; dual charger, @ 80 amps, 58 miles/hour charge). Again, for a single charger @ 29 miles/hour charge - that's about 9 hours or overnight from close to empty to full.
I'm not sure if you're asserting that the UMC and HPWC charge the car at the same rate, given the same amperages. The UMC is limited to 40 amps, so dual chargers don't help at all in that case. But if a HPWC only delivers 40amps, it's no different than the UMC.
Also, I think very few people are draining their cars to near zero every day, and charging to near-full overnight. That's an extreme edge case. I have a NEMA 14-50 (which I plug and unplug all the time without incident), and if I plug in at night, it only takes an hour to three to recharge up to the limit I've set. So unless some owner is driving 200+ miles every single day, and has less than 8 hours to recharge their car, the 40amp UMC on a NEMA 14-50 works just fine.
OTOH, the HPWC looks much cooler if you have the $750 to spare.
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Yes. I've charged at 70amps with the J1772 adapter, on Sun Country EVSE's which are common up here. I've never seen 80amps EVSE's but if there were, it would work. 100amp wouldn't work since the maximum with dual chargers is 80amps (2 x 40amp chargers).
Yeah, I didn't mean to imply that one could charge at 100 amps, just that if the EVSE is a 100amp service, it's still usable (up to 80 amps) using the J1772 adapter. But thanks for clarifying that incase I was unclear.