Just in case anyone reads this at a later date, I've just made this cake -
Result - it's OK. Not as good as Tesco free from chocolate cake slices, but OK. Considering the price (not sure how much rice flour is in the UK, but it's only 30p a bag here in Cyprus (staying with my parents for a few weeks), I'd definitely make it again. Will have a go at freezing some of it, as it's massive.
I didn't have a proper cake tin, so used a baking tray that we use for roast potatoes. Hence it's bigger and flatter than it prob should be.
It took longer than an hour to bake in our gas oven (which is new, but the bottle is going so maybe not as hot as it should have been).
Have had to cut the 'crusts' off, as middle is moister and nicer, so if baked in a smaller tin, there would probably be more middle IYKWIM!
Also, I made the batter, and then had to go out, so it spent the night in the fridge before cooking. Might have been nicer if it hadn't! The mixture was reallllllyyyy thick, so don't be surprised by this. Mixer on top level struggled, so don't try this by hand!
Good luck if you try it!