You want to be very careful when using ty-rap guns.
If set up incorrectly (or used by the wrong person), that can do serious damage to the insulation on some cable types, especially some of the more modern lightweight cables.
I know that some aviation companies will not allow their use for this reason.
Another possible problem with their use is that not all of them will do a true flush cut when trimming off the excess. This leaves a small very sharp bit of plastic sticking out, which as many A&C's will confirm, can be as hazardous (and as painful) as incorrectly applied locking wire.