I recently purchased a Yonanas & paid £35 (free delivery).
Good points:
It does actually make a tasty (sweet) desert that is like a cross between IceCream & Angel delight
Its easy to use... add different sauces/ingredients too
Easy to clean/store
Is very safe
Bad points:
Its very loud... maybe on par with a loud blender
Its a bit hard at first to get used to how soft you need to make the bananas before you put them in... too soft and you just get like a goey mess that hardly comes out, 15 secs on defrost(microwave) I found the best for my frozen bananas before putting them in
You need quite a few (maybe 2 or 3) bananas to get a reasonable amount in your dish, I found 3 gives me about half a dish full & that's with scrapping the excess from inside the machine too. Obviously if your adding other ingredients then you probably won't need as much.
Over all I would give it 7/10 & I am happy with it. As with all food preparation appliances practice makes perfect so don't expect perfect results the first time.