I need to remove the rear quarter windows and front windscreen from my 3 door cosworth, i bought one of these tools hoping it would do the job

http://cgi.ebay.co.uk/Windshield-Car...d=p3286.c0.m14

Ive been out in the car for about 2 hours today trying to cut through the glue stuff that holds the rear quarter glass in but seem to be getting absolutely nowhere with it!
Have any of you ever used one of these? If so is it just a case of being patient with it or am i better off just getting a proffessional round to cut them out for me?