My stihl is now about 15 years old and has cut up an enormous amount of logs. Original bar and on its 3rd chain. I would say cooking oil works fine.Each to his own but I just don't get why anyone would run cooking oil just to save £5-6 on 5L of oil. I would bet money that chain/bar/pump wear would outweigh that cost.
If you let the machine run dry you won't have any issues but the people who just bin them when they won't start can't be bothered with that hassle.
I sold my last 25L drum of chain lube on Ebay. Would never go back to it.
Only drawback with cooking oil is you do use a bit more of it. Also great for the environment.