The 2/0 is the hook I use when replacing many of the hooks on my bigger bass lures, generally it is a 1, 1/0 or 2/0 on all the UK's favourite bass plugs.
The Decoy Pluggin' Singles are designed to replace treble hooks on lures with singles. They have an over sized and upright eye to allow for the split ring.
Many anglers prefer only having one hook in a fish, rather than a treble to contend with. Other advantages with the singles is that they allow the lure to work more freely.
You were one of the very few shops to have them.