Water-methanol injection is actually very, very safe. How else can you make more hp & Torque, increase mileage, and get significantly lower EGTs (200-250deg F)?
There can be problems, as mentioned. If you use more than 50% methanol (which we don't recommend), you can have diesel knock. We have dynoed with 70% meth 30% water for testing and had no problems, but we did have a customer with 3 stacked controllers who had some knock running 50/50. His timing was so advanced it isn't even funny. That moderation advice is very wise, and this guy wasn't about to listen to it.
If you run propane AND water-methanol together you are injecting a whole lot of easily combustible fuel, and you will run that diesel knock risk again. We have found if you keep the methanol down to 25% in the water-meth mix, you can use it with propane just fine.
Unlike propane, if you get the quantities totally wrong - meaning you way over inject fluid, you won't hurt a thing. You quench the flame and basically get an ignition miss, but it doesn't hurt a thing. With propane, if it goes wrong, your engine goes boom.
The water actually does lower the peak CP's, but extends them out longer (pushes on the piston for a longer physical time) so the mix of water & methanol work great together to keep CPs very safe while making more power and burning more of the diesel instead of sending it out the pipe.
My last comment is that if your PMR are only good to "XXX" hp and you go over that, it isn't the programmer or the exhaust or the turbo or the water-methanol that broke the rods - even though the water-methanol might get blamed because it was the last thing added. What broke the rods was simply too much power production for a given rod.