They never need adjustment as it is a siphon, they can and do fail over time though. I ran a system with one for over a year and reprimed it about once every two weeks to be safe, zero issues.

When I rely on it I make two they are cheap to make so why not. 2 is 1 and 1 is none and what have you.

I also use them as back ups when I do use a bulk head, again cheap and easy to make. The key is they have to be level to keep tanks equal but they work incredibly well.