I just finished my install of Razors kit, still need to do some tuning, I've worked it up to 25# with zero knock, but its running on the fat side. I'm going to tune it down to 23-24#. As far as blowing head gaskets, doesn't matter what fuel your running, after 25# thats a lot of pressure, keeping knock from occurring doesn't mean the pressure in the cylinder is not rising, eventually there is a limit no matter what.
The progressive kits of today are light years ahead of those from years past. Most failures have to do with the pumps, all thats needed to resolve having a head gasket blown if your alky pump fails or you run out of alky is 2 pressure switches, if boost is past x level and alky line pressure falls below x level, then cut the spark to the motor...makes it fail safe.
Most blown motors are due to trying to push the limits of your motor and failing to tune properly. The alky kit is not a bolt on and go kit, you need to know how to tune or you will be playing with disaster.
Also, once tuned, make sure all of your boost settings and the alky controller settings are marked inc ase you happen to hit the controller with your knee and turn down the ramp multipler of the alky.
Also, using methanol over the old school rubbing alchohol is a very big benefit of the new kits over the old ones.
If anything else, it s great insurance even if not running the high boost #s.