The problem is all these devices mean you must still go outside and check.
All a waste of money. As the cylinder runs out whilst in use you get a warning. Smell and flickering flame. Out you go and swap cylinders. 😜
The Truma system had a remote indicator.
I prefered to use an automatic change over system, (in the days of regulators on bottles) where one regulator was designated the main, and the other as reserve. There was a bottle pressure indicator on the main side, so you could quickly see when the mains had expired. If you checked daily then you'd quickly detect when the main had been used up, and that indicated time to replace it, which automatically reconnected the system to the new full main bottle.
Using this system it took me literally years before the reserve bottle was nearly empty.
After using it for a few trips. I gained a sense of how many days the main bottle would last so I knew when to start checking.
I also used a bulkhead change over system for a long term continual test project, which indicated when it changed over from bottle A to B or vice versa. Simply had to disconnect and refill the empty bottle. In my opinion this was the better system as each time you changed a bottle it was always full, and there was no concern about how much may be left in reserve bottle.