I love the SeedSigner. You pull ou tthe SD card after it boots. Then you scan the seed, which is a QR code on a piece of paper (so you can't easily lose your seed). When you disconnect power it forgets everything.

Only problem I've had is getting my computer's camera to focus on the QR code it presents. Sometimes I have to fiddle around for several minutes to get it to focus and scan it. Because it is so small, the camera wants to focus on things behind the seed signer. It needs something like an 8x11 sheet of plastic that shrouds it so the camera can't see anything at any other distance.