USB Powered Foldable Soft Piano Keybaord with Built-in Speaker

Pros: This keyboard can handle 4 keys at the same time. Most foldable ones can't. It can be foldable into a fairly small package (when on travel it's really handy). Also kinda plays on non super flat surfaces.

Cons: The arrangements aren't of the best quality, every time you need to reselect the one finger or multiple finger cord settings. Sometimes hard to press the button.

Other: If you want to travel and you want a portable piano, this is one of the better ones to have. You can have some fun with it while away.

Pros: It's foldable, so you can store it wherever you want
It's a perfect gift for kids, since the keys will not fall off and the kid will not break them (unless he uses scissors)
Sound is not the best quality, but it's not awful either.
If you run out of batteries, you can power it using a USB port, so you could probably use a powered USB hub without connecting it to any computer, or use a USB to wall outlet adapter.

Cons: Mine came without the USB power cable, but I had a spare one from a wireless mouse.

Other: nice keyboard for a very nice price.

Pros: A very good toy. As it is flexible, it does not suffer much if kids sit or step over it or do thing like that (you can never know what a kid will do with a toy). Sound is OK, you can choose some different instruments. Price is a little high, but comparing to Brazil, it's nice.

Cons: Sometimes the keys doesn't respond to touch. If you think it as a toy, you won't bother, but I cannot use it as a real musical instrument. Anyway, if you want to play the piano, I believe you should look for something else. I bought this to my 1 year old kid, so that's not a con for him, I think.
The plastic box, where the speaker is in, is not very well built. Not too resistant to children.
No manual, there are some function keys that I don't know how to use. Again, as my kid can't read a manual, he did not care very much. He just want to hit the keys and hear the sound.

Other: Ok for small to midsize children. It is a nice toy, but not a nice piano.