I'm not sure I agree that they're mechanically complex. They're engineering 101. A pump, a heater and a thermostat. They're rather mechanically simple.
> Dual boiler machines generally cost thousands even for small home machines.
The _cheapest_ Decent is $3500.
> Commercial dual boiler machines will set you back at least $10-30k, easily.
You don't need a $10k-$30k machine to get a competent dual boiler. If you look at something like a Lelit Bianca, a dual boiler with preinfusion and flow control while $500 cheaper than the cheapest Decent, you can pull your first shot in 10 minutes. A home brewer making espresso on a Bianca isn't going to notice the difference on a $10k or $30k machine because at that price point what you're paying for isn't the ability to pull a shot, it's the ability to pull thousands of them every day of the year.
> But they basically haven't changed since the sixties.
That's true but I argue they don't need to. We don't need to iterate on everything. Technology doesn't always make things better.