Rubaiyat is an unrefined apple. At it's best the flavor is excellent, but getting flavor/ripeness and good texture all in one specimen is rare in my experience. Like other very red fleshed apples, it has an amazing berry type of flavor, but it is a work in progress like most if not all of the red fleshed apples released by greenmantle probably are. After all, Etter did not release them. Excepting pink parfait that is, which is pretty awesome, but only lightly tinged pink. Rubaiyat is also very susceptible to scab in my limited experience. Who knows, it may do better elsewhere. If you can score a scion, I think it's worth trying for the sensational factor alone, and I'm sure it' makes great juice, but I wouldn't really recommend to buy or plant a whole tree. I feel pretty much the same way about Grenadine, though I think grenadine might be a little better culturally speaking. I think some of these won't do well in some climates too, but maybe that goes without saying. I got my first red fleshed fruit this year from using using grenadine as a seed parent. I'll try to attach a picture.
Time will tell, but I'm hoping it will best Grenadine. I'm also using Rubaiyat as a parent. I think both are more refined than most red fleshed crabs probably are, but they still need a lot of work. I just figure Etter started the job and now we can keep his work going by using his partially refined seedlings as parents instead of starting with the most primitive red fleshed crabs.