Not at all bad. I dunno if it's the oil (we used olive oil) or the GF flour that made it slightly rubbery, or if it's just like that.
We did one a second one in a bowl and it didn't really rise but was perfectly edible, esp with ice cream. It was easier for Jack to do the mixing in a bowl, and the first one had risen alarmingly... bigger mug or split the mix between two, I think.
We're going to give the recipe to Jack's school, it's ideal for the kids' cookery sessions.

Oh, yeh: we used drinking chocolate instead of proper cocoa, may not have helped.