> ~100 lumens per watt is rather poor

Is it, though? Most of the LEDs I've seen are very similar, and lower temp LEDs are slightly less efficient. If it were 60lm/watt I'd be a bit surprised, but 100lm seems pretty typical. Maybe not "well engineered", but average. (Which, with all due respect to the founder, seems the quality of the product.)

CREE offer a variety of LED types with efficiencies 150lm/w (eg CMB, XT-E), up to 230lm/w (eg, 5050).

While 100lm/w is typical for domestic LED lighting, it's going to cause problems when the total power is several orders of magnitude higher but the form factor is approximately the same size. That heatsink will probably fry an egg, and I wonder about the lifetime of the diffuser plastic.

fwiw, LEDs with higher CRI will generally be less power efficient, so the premium category has a 3-way tradeoff between brightness, power, and color quality. It's common for high efficiency LED lightbulbs to be much worse at illuminating red objects.

True enough, although CREE's XT-E offers 140 lm/w at a CRI of 80 and a colour temp of 3000k.

I assume this product has not met any regulatory requirements, because selling a ~600W hot plate suspended at eye level cannot be legal.

These LEDs are just the ones found on imported LED strips. Adjustable colour temperature is a novelty that is not compatible with LED efficiency or lifetime.

CRI of 80 is not great. From my reading, you want CRI 90 if you want light that's pleasant to exist in.

Fair point. Given that this product has adjustable colour temperature, I really doubt all of the lumen, CRI and watt values. It sounds like the designer also got stung when the chosen LEDs didn't give the expected power output.

The 'wasted' electricity is turned into heat, which should be welcome by their target customer base.

I can't imagine the customer base for people who want a ~600W metal disc suspended at eye level is very big.

Q: Does it get hot/how is it cooled? A: It's cooled through our large heatsink and ultra quiet Noctua fan. The fan only turns on above 75% brightness. At max power, the heatsink is cool enough to put your hands on it for a couple of seconds.

It's still dissipating near 600W. "I can put my hands on it for a few seconds" tells me it's dangerously hot and would not pass any kind of safety certification. How many other objects do you have in your house that heat up to a similar degree? How many of those objects would you like suspended at eye level with no particular safety guards?