In the US the "bittering agent" in ethanol is usually just some other organic solvent and is generally referred to as "denaturant", hence "denatured alcohol". The purpose is simply to render the ethanol undrinkable so that it can be sold cheaply and not taxed as if it was liquor. The amount of denaturant used varies, but 5-10% is common. Isopropanol at 5% was used in the ethanol we bought at one place of employment. Check the label or MSDS of whatever ethanol you buy just to be sure, but most likely the denaturant will not cause any problems.
You misunderstand. I'm not using the term "bittering agent" as a generic and inaccurate synonym for "denaturant". I know exactly what denaturing is, its purpose, and various ways it's accomplished. Adding non-drinkable solvents (which may or may not be bitter) is one way. It's not the only way.
I specifically said "bittering agent" because that's specifically what I am talking about. It's not a solvent, it's a chemical additive. (Its name is "denatonium", presumably derived from precisely this use case.) It leaves aggressively bitter-tasting residue on anything - readily noticeable on fingers even after a regular hand washing. (It takes a surgeon-style hand washing to really get it off.) I have no information on the electrical properties of denatonium residues, so for anything permanent (or sensitive, like high impedance areas of multimeter boards) I use proper flux remover.
Yes, using such cheap industrial alcohol is crap, but if you saw how expensive IPA is here, you'd use cheaper alternatives, too, where possible! :p (It's actually sold as decorative fireplace fuel.) IPA costs so much, it's actually only insignificantly cheaper than commercial flux remover like the Kontakt PCC!!!