To the OP.
The problem with the one you’ve just broken is the materials are relatively cheap and weak. A combination of the ‘pin’ part wears, the hole wears, and the wider swaged part wears (and isnt that much wider than the hole to begin with) … until it will pull through.
(For me the spring / gate fails or wears out 1st instead on those types).
Best couple I’ve had, have this end piece from Ruffwear (like on this lead). The jaws interlock too so no inadvertent opening. Yet can still be done 1 handed.
Ruffwear – Crag Leash
Or the non-stop-dogwear ones with a swivel and gated carabiner.
Non-stop Dogwear – Touring Bungee Adjustable Leash
Im using a Ruffwear ‘front range lesd on my Labrador, which I realy like as its got the gate rhat only opens sufficiently in specific places, and secondary slider to prevent inadvertent opening.
But its not been overly tested in tension loading as my fella generally doesnt pull much (i can’t abide having my shoulder pulled out, so I’ve (mainly… he’s still a pup albeit 20kg+ and rising daily of pup) convinced him it annnoys me and life is best when im not annoyed !
For the one linked from the Chandlers earlier:- whilst plenty strong, I’d be mega wary of the spring pin being pulled open by accident and hey presto the shackle instantly pops open and your dog ends up….wherever he wants to be… butchers, bakers, or in the middle of the busy road (my parachute has one of those designs of shackles on one element, precisely to allow mega quick 1 pull detachment of a bridle line)