I've worn the palms of my hands out along with the handles of my isky tool.
There okay, for occasional use, or as a stepping stone to a BHJ tool.
If you want to work your arse off, make a wide cutter to do fire ring grooves for a isky. I've done that to about 6 blocks, it's a workout.
A friend of mine has had a BHJ for a year or 2, the isky doesn't get used on Cummins engines anymore.