Yes. Used one of these for years and were given two when we collected the van in our goodie pack.
There are conflicting views on their usefulness and they certainly won't take the place of an internal monitor. Our dealer wasn't all that keen on them as he felt it was difficult to be sure they fitted without leaks but we have since fitted them on both gas bottles and all is ok.
The greatest benefit to us is the quick ability to get a rough idea of how much gas is left in bottle but that can be done with a jug of hot water.
Just remember that the fuse needs at least two pumps when gas is turned on.
We also have an internal gas leak detector so don't rely on the fuse to indicate a gas leak.
For safety I'd go for the gas detector inside the van but the fuses do have their uses.