Here are some comparison tests of the Tesoro Sand Shark, White's Dual Field, Detectorpro Headhunter Pulse and White's PI 1000 pulse induction metal detectors. They are tested in the manner recommended by Eric Foster. I do not claim to be an expert and make no value judgements.
http://www.youtube.com/watch?feature=player_embedded&v=g5wDQnDi_wE
http://www.youtube.com/watch?feature=player_embedded&v=RfAOJTAAV4w
http://www.youtube.com/watch?feature=player_embedded&v=8Dch7XjHcSE
http://www.youtube.com/watch?feature=player_embedded&v=q951fA2lMW8
http://www.youtube.com/watch?feature=player_embedded&v=g5wDQnDi_wE
http://www.youtube.com/watch?feature=player_embedded&v=RfAOJTAAV4w
http://www.youtube.com/watch?feature=player_embedded&v=8Dch7XjHcSE
http://www.youtube.com/watch?feature=player_embedded&v=q951fA2lMW8