I have seen the La Caja China roasters. I've also had pork out of the Caja China roasters. Easy, simple roasting but the meat needs some smoke IMO.
I just fabricated a Santa Maria cooker and modified it to also be a La Caja China cooker. I will be testing it with some pork butts in a week or two.
My cooker is all steel and I plan on installing a smoke generator on it so I can get some smoke flavor while roasting the butts, hog, etc.
Yes, I'm sure there is a ton of fuel waste, but, I have fabricated a grate to go over the charcoal during the roast in case i want to grill or keep something hot during the roast. Caja China also offers an optional, over the top of the charcoal grate.