Hard to beat an MB Crunch Proof Swivel , lightly welded, IMO.
Any 'quality' swivel /double swivel added to a trap / trap chain is an improvement (again, IMO )
I believe most trappers worth their salt would agree to that.
Rod swivels are a good investment, but depends on who made them.
All traps mods, are not created equal. Same goes for stop shocks.
I even add an 'in-line' swivel to my snares, plus a double trap swivel at the anchoring point.
Swivels are an added insurance.
Now Mike mentions having 'possums , (of all things ) bound swivels up with grass.
That comes from two things.
Having a short chain on your traps ( and /or ) having long grass with reach of a trapped animal.
I have for years, taken a push mower and/or a weed eater and cropped the grass right down to the ground where I intended to make a set.
Now that isn't every location, mind you, but it is a lot of them.
Not uncommon to see a 6 foot mowed circle in an area of otherwise long grass.
Does that stand out ?
Sure. And . . . because it does an animal will walk right to it.
Vegetation doesn't grow much , (if at all ) in late fall and winter conditions . . .not here in the northern states it doesn't.
This is pre-season work. Level it, then come back in a week and make your sets.
Far easier to re-make a set in short grass than in grass a foot tall.
I often take a drill, with a 2 " bit and auger out a foot deep hole the day I mow.
Often pre-baiting it with fresh meat
But, I digress . . .