[Butcher]

Dunno if I'd call propylene glycol "safe", there's definite questions over it's long-term effects on health. Safer than most other additives though.

Personally, I'm not that worried - I don't have kids, my hoses haven't suddenly wasted away from water wetter or any other addivitves (mind you I don't use the cheapest tubing in the shop). Nor have my hose clamps suddenly snapped in half allowing the hoses to work loose. I've had only one leak on an installed system, and that was evident immediately so the system wasn't on. I corrected the issue before it became a problem.