I wouldn’t say it’s rare, since I’ve seen them sold at Home Depot / Lowe’s. Haven’t tried it myself though so can’t comment on the flavor. I did do some research on tropical guavas a while ago when I was considering getting a tree (I haven’t done so), and Mexican Cream came up as one that most people spoke favorably of.
I dug up an old link that I remember seeing on this forum which mentioned this guava and compared it to a bunch of others: