It is actually more complex than the comments here. My personal view (having played around with some) is that they probably show zero benefit on fixed wiring because fixed wiring does not initiate arcs, even with loose connections. Loose connections either make a connection or not, and as 230V can only jump about 100 microns at best, and even if it does a big hot arc cannot start unless it is already a big enough arc to melt the wire or terminal (the electrodes) to produce an ion source, otherwise nothing much will happen. This is clearly illustrated by the product standard and demonstration jigs the manufacturers show around to get sales. The test rig and standard both depend on one electrode being carbon (which ionises very easily) and moving the electrode(s) to actually start the arc with an essentially short circuit. As we do not have carbon wires or terminals, and the manufacturers do the series test with a wire cut but the sheath burnt (carbonised) to start the arc (see product standard). Various makes detect arcs started in various ways but do not detect sparking of motor brushes, and vary a great deal in sensitivity even with the jig. There are lots of YouTube videos where they are tested by the trade. None of these manage to get a trip with a metal-metal arc however hard they try. Note that arc welders depend on the easily ionised electrode coating to get a reasonable arc, it is virtually impossible with uncoated wire in air. Burnt, welded etc terminals are caused by resistive heating not arcs, so almost never cause a fire unless there is much flammable material nearby. Thermosetting boxes and accessories are very hard to get burning (that's why that are made of thermosetting material).

It is actually more complex than the comments here. My personal view (having played around with some) is that they probably show zero benefit on fixed wiring because fixed wiring does not initiate arcs, even with loose connections. Loose connections either make a connection or not, and as 230V can only jump about 100 microns at best, and even if it does a big hot arc cannot start unless it is already a big enough arc to melt the wire or terminal (the electrodes) to produce an ion source, otherwise nothing much will happen. This is clearly illustrated by the product standard and demonstration jigs the manufacturers show around to get sales. The test rig and standard both depend on one electrode being carbon (which ionises very easily) and moving the electrode(s) to actually start the arc with an essentially short circuit. As we do not have carbon wires or terminals, and the manufacturers do the series test with a wire cut but the sheath burnt (carbonised) to start the arc (see product standard). Various makes detect arcs started in various ways but do not detect sparking of motor brushes, and vary a great deal in sensitivity even with the jig. There are lots of YouTube videos where they are tested by the trade. None of these manage to get a trip with a metal-metal arc however hard they try. Note that arc welders depend on the easily ionised electrode coating to get a reasonable arc, it is virtually impossible with uncoated wire in air. Burnt, welded etc terminals are caused by resistive heating not arcs, so almost never cause a fire unless there is much flammable material nearby. Thermosetting boxes and accessories are very hard to get burning (that's why that are made of thermosetting material).