I have been using iDefrag for a couple of years now and have had nothing but good results. It will take quite some time to do its job, but that is to be expected for all that it does. I have used it many times and have complete confidence with this application. Just don't expect iDefrag to do its work in a matter of minutes. Start it, let it run all night long and don't get impatient.

Tech support is also good the one time I needed it.