It's a matter of taste, really. On the one hand, your disc is less likely to suffer abrasions than with a tray-loader and the slot's velvety curtains make sure dust and foreign objects don't reach the internals. If you want to mount it sideways, you can, and you don't need to mess around with the fiddly and often useless tabs on a tray-loader. On the other hand, you'll probably end up getting fingerprints on the disc unless you're very careful and there's no emergency release, so if it goes belly-up during use, you'll need to take it apart to get your copy of Quake III Arena back. We had no problems with installation, but were disappointed with the noise of the drive during use.
Performance is good, though, with fast access times and CD read speed results.
A nice package if you want a slot more than a tray.