Just received an unofficial PW black leather case for about USD 10.
It works and has the sleep function. The leather is likely fake (doesn't smell like 100% leather, but still feels ok). There is no magnetic closure to keep it closed weak and so the cover does not remain firmly closed as with the official cover.
There is a sleep function when you close the unofficial cover, but because of the lack of magnetic closure, you need to deliberately/briefly hold the cover shut to ensure the sleep mode is activated.
The leather doesn't have the same build quality. The original's leather is overall more sophisticated, being textured and softer.
The back part of the unofficial cover is hard plastic but thinner than the official one. It would probably provide less cushioning in a fall situation. Also, the PW clicks into place at the corners by four hard plastic corner brackets, and it's very very tough to extract the PW once it's in. The official case allows for much easier extraction, because it has a slightly rubbery rim clasping the entire edge of the PW.
For the price the unofficial cover is very good value.