I have a friend that has been using amsoil on a 2009 hyundai. Said it made a huge difference. It was a used car with unknown service record.I have purchased motor flush products in the past when stocking up. Those bottles sat n sat unused in the cabinet in my garage for very long times. Even Amsoil's flush treatment "for engine and transmission use" was among those I had accumulated at some point. They were eventually given to someone with an older engine or to use before they opened up an engine for inspection, repairs or rebuilds. I never could get myself to put those in any of my engines. Never got to the point of needing a real "flush" tretment product anyway since the 70s. Now I would just use an oil to do it.
I'm also not comfortable using anything like that. If I had some serious issues, I would and hope for the best. LiquiMoli is used alot by BMW people as I read on amazon reviews and the boards. I don't think either of these two products will ruin a car, but I would not use them unless I had a real need. I'm curious how my car would do with one. I used to change the oil at 10k for the last 100k miles. Very curious to see what the oil would look like if I did the liquimoli.