The problem with slide phones is the traditional cases have to be in two parts. They rarely fit well and are prone to dropping off. Pouches only protect the phone until you get them out to use them. So this flip case was the best solution. I wasn't going to pay £20 for one with Sony Ericsson printed on it, so I chose this one.
Works very well. Has a good grip on the phone, and doesn't get in the way during a call. No parts of the phone would be vulnerable if you dropped it.
It also had one unexpected bonus. If you open the flip cover round a full 180 degrees and fasten it back, it makes a nice 1 inch gap for you to slide your hand into when holding it. It also means if you place the phone down and use the speaker to play your music, it holds the phone off the surface and music is much louder as a result.