Belt reels are designed as either a back-up to the reel on your gun or as an alternative.
If you've got 50m of line on your gun reel and shoot a big fish at 20m plus there's a good chance it'll have you spooled by the time you reach the surface. These belt reels are just the insurance you need to have the confidence to take the shot.
This is the same indestructible Rob Allen Vecta Reel but it is fitted to a solid stainless plate that attaches easily and quickly to your belt. The clever bungy system allows you to remove it without taking your belt off and with the handle you can quickly attach it to a float while the spool is spinning if s--t gets real.