"Don't eat it! Don't eat it!" I did! I even went back and picked the other one the next day... 
I'm bored... can you tell? I have no clue what type of Cactus it was from... they grow all over the place here in Arizona.. real tall, pretty pink flowers.. the fruit kinda smelled like a peach on the outside.. and just fruity on the inside.. it had lil black seed type thingies.. like a kiwi. It didn't taste overly wonderful but wasn't yucky either. I wouldn't mind finding some other Cacti fruit to try. 
So.. if you ever get the chance, give it a try..