As an avid Mark 1 detectorist for 20 + years --i am addicted to the tone id --and the target id reads good to 8" in low minerlized ground ---anyone have their opinoin of the 3 filter /4 filter units ---of all my years i have never tried the 8500b , Eagle , Condor ,9000 , --- how do they compare to the Mark 1 in sweep speed and overall performance? i am thinking about the Eagle --dont know if its a 3 or 4 filter unit -your thoughts appreciated , rick