Cheap 10A/20A MPPT

well, the cost per ampere is more than I paid for my 2 victron 75/15 controllers, so they ain't that cheap..

I tend to go into "over-spec".

Today's chargers, controllers and the like seem to have trouble dissipating heat when used towards their max parameters.

I just ordered a second one of these, being pleased with the first I bought a couple of years ago. More money but I know it works and it barely gets noticeably warm. It lives it the tornado that is my air-cooled camper engine bay with 1 cu m of air + rain whistling round it every second at full tilt.
Even this yank grudgingly admits it's "ok for Chinese tat". Lol.

err ..............  my mistake, I was looking at 75, of course 15 is the relevant value.  They are about £70 each, so more expensive.

Not everything is Made in China. The USA still makes some good stuff. It's remarkable how easily the Brits are willing to roll over and 'play dead'. Start making your own quality products. "Brexit means Brexit" says Teresa (who voted 'Remain').