Got my MKettle today. Yes it's small and yes it holds 500ml!
Just tested it with my Whitebox Stove and from bloom to boil with cold water at 10c outside with no wind, I had a rolling boil in 4 mins flat. Not tried solid fuel yet though. My home-made pop can stove, Budweiser Stove and mini bull stove also works.
My concern at the moment is the longevity of the neoprene sleeve which is in direct contact with the metal containing the water. I can see the heat degrading that fairly quickly?
It's a double edged sword really as you have to weigh off the compact size (which is a lot smaller than the Maverick) against having to source a new sleeve whenever it expires.