The Argos has a 600ml boiler + PID which works very well, though it requires a specific workflow for 2 or 3 back to back milk drinks (and if making 3, steam pressure on the final one will suffer) and constant (currently manual but designs are afoot for an auto refill system) refilling.
I’m thinking of something I can run from an inverter, in turn powered by a battery bank.
The appeal of the thermoblock is that it heats a lot less water for a lot less time than a conventional machine.
But if they’re all shit- plan b.