I grew the Mayan Twilight this year but I'm afraid I can't say too much about yield because I don't go weighing them or anything.
I can say they grew well in a totally scab free condition against mighty difficult odds - earth being dry as a bone. About half of my spuds were scabby and all of them a very modest size this year.
I was thinking of adding the Mayan Gold to my list this year - glad to hear they're good I'll certainly be getting a few. I raved here about the Twilight before, but worth mentioning again. I ate most of them as baby potatoes because they had a really intense chestnutty flavour, delightful
Texture wise, they are slightly more grainy than a normal potato and you're right they're different and must be eaten fresh so you wouldn't want to grow too many at once.