I have the 7" Gradient Lense Hawkeye borescope that I bought not working. Had batteries grown into the barrel of the light source, which turned out to be a Mini Mag Light. $12 fixed it.
I've also used a 17" with the 90 deg mirror attachment. For rifle work, It is many times better than the 7".
Never looked through any other borescope, but will never let my short one go unless I can get a 17" one. Both of them have the small tube that goes in a .22 cal bore easily, and I believe that they will just barely go in a .17 cal bore, but am not positive.
Bottom line, its one of the most useful tools I have.
Tom