Maybe I can explain the issues in using non-toxic propylene glycol versus ethylene glycol (regular or ELC antifreeze) If you drink it, the regular antifreeze will act pretty much the way alcohol does in your bloodstream, taking the place of oxygen in your blood. This will starve your muscles of oxygen and eventually kill you. The cure is to pump alcohol into your system in slightly less than a lethal dose so it pushes out the ethylene glycol to be destroyed by your kidneys and liver, and then eventually after 24 hours or so, letting the alcohol get cleaned up by your system much as if you had had a whole bottle of tequila. .....If they got to you in time you'd have a bad time but you would live.
If your dog gets into it, because of the sweet taste the dog will lick up everything it can get, and very quickly get such a high dose it won't survive.
Because of all this, the conventional standard is that if a failure will lead to antifreeze contamination of drinking water, you use the non-toxic, but if a failure will only lead to leakage out of the system you use ethylene glycol. Hydro-hot/Aquahot/Hurricane/ hydronic heating systems for coaches come in a number of configurations: on mine the domestic hot water runs in a copper coil which is wrapped around the furnace body so ethylene glycol antifreeze is fine. Some have a single wall heat exchanger where a leak will result in contamination of both streams with the other, so propylene glycol non-toxic is used. From a post above, an option was offered at one point to have a double-walled heat exchanger which technically would be fine with ethylene glycol. but for efficiency it would probably have some liquid in the centre, and two failures would result in cross-contamination. Since that's not something I would expect your routine maintenance to detect, I'd recommend the non-toxic for those as well.