I tried this with my A500 plus a few days ago, the keyboard in particular had yellowed quite a lot.
Just after a day I could see the keys were less yellowed, without even taking a before photo. I will get it out in the sun again when I get chance (and when we have some sun here in Runcorn).
If it works, I am going to have to employ a security guard in my back garden with all this hardware outside
