Yes, sharks do make me feel uncomfortable when they are around. The fact is that when one has a job to do underwater, a job that requires a full concentration, it is simply not possible if those killing machines are there. I am not sure if these give 100% protection but U.S. navy is using them and there are independent tests done too and according to my experience they work.
We were using those with full wet suits and also with dry suits and Interspiro Mk2 apparatus, not just a full face mask but the whole apparatus.
I do not care what those romantic shark lovers say, sharks are wild predators who act according their instincts.
Salud
Finn