I liked the sound of McDougalls' thickening grains, until I looked up what they are made from.
The ingredients are given as potato starch, maltodextrin, palm oil, dried glucose syrup, emulsifier (soya lecithin).
I have no problems with the potato starch, but maltodextrin and glucose syrup are sugars - what are they doing in a product like this? Palm oil without details of its source are a bit iffy, and at a personal level, anything soya based, even processed to make something else, are banned in our house as DDiL has a soya allergy, sufficient to need an epipen, so I avoid anything that I could accidentally stir into a dish without thinking.
I have recently started using porridge oats as a thickener. They work very well in slow-cooker meals because I put them in at the start of the cooking and they cook so long, they completely disintegrate to give a smooth thoickened sauce. They work pretty well in other dishes with shorter cooking times, but I have yet to use them in a cheese sauce or sweet sauce, I only use them in gravy.