Contrary to what people say on newegg, it is extremely fast, getting about 60 MB/sec sustained from the hard drives that it is attached to, over the IDE bus on the same computer I would get about 50 MB/sec sustained. Absolutely love the device.
Depends on the IDE controller that is onboard. In my case I gained some speed, which really is negated when the drive is not doing just a straight read from /dev/null write to the hard drive. As soon as it has to scatter read/writes again, the speed improvements will be negligible.