Yes I have used it and effectively separated different minerals. You can reach upto 4.2 density using dilution technique. Advantage of this method is that you can recover the chemicals after your use. You can also try Bromoform which is easily available for density upto 3.5. Since the thallium salts are highly toxic import of the chemical is very difficult. You can contact with some UK base agent from Internet. If you fail to import I shall try to help you.