UDL 30 Plastic Underlay requires flat head nails. I know most people wear braces, but they get blown away by the wind. I discovered this the hard way. Now I only use cap clips for things I want to remove later. Having to hand hammer in cap nails on my newest roofs I bought this. It might be faster than the Stinger cap stapler because I have less fiddling with it than the Stinger. After a learning curve adjusting the height of the spool holder (it didn't feed the nails properly until I got the height adjustment right) I think it failed once or twice on a whole box of nails. See evaluation of the nails. I looked at two manufacturers. The other was twice as expensive as Bostitch. Easy to use, lucky because there are a lot more nails in a strand than there are caps in a stack. If I drop it off the roof and break it, I'll buy another one without hesitation.