.Why not?
They vary slightly in quality, i'd want brass or bronze snaps [not nickel-plated or chromed steel, which will rust],
but otherwise, they're all practically identical -
nylon-coated metal cable for trolley & drop-line, a spring-coil to absorb impact, 2 stops so the dog can't run around the 'posts'.
The main issue I would have with those trolleys is the hardware. Not a fan of the flimsy looking spring. I wouldn't use chain or wire of that size to contain a dog of any size, and if the dog pulls the spring taut, that is essentially what it becomes. The turnbuckle on the one shown might be 1/4" diameter? Average WLL of one of those is 500 lbs. MUCH less than the cable. Both those components would have to be much beefier in order to be sensible for the size/strength of dog they are advertised for if used as a straight tie out- the saving grace is that with the trolley the force is more evenly distributed/dispersed between the length of the cable and two anchor points, but it's still careless manufacturing. I'm not really a fan of brass for tie out conditions, as it's soft and will wear fast when abused (ie: if dragged over any substrate/doghouse, or even brushed repeatedly against collar or tags), not familiar with bronze in that application. The other issue with the cables shown is that IF the dog stretches the cable sufficiently as to bend the eye tightly around the snap, that sort of tight flexion can weaken the cable significantly (up to 1/2 if the two are the same diameter). Might be better with a thimble in the eye, which also prevents some wear and crushing of the wires. I feel like the coating on some of these cables can go either way- does provide some abrasion resistance and you probably would find it difficult to use non-coated wire for pet securing purposes, but I have also seen moisture/condensation under said coating before, and you can't tell what state the cable is in under there. I would be fine putting my current dog on the trolleys pictured, but he is about the size of the cat pictured, and I wouldn't trust it with dogs like my previous large dogs.
they're straightforward to install, & surely sturdier than the 'nylon leash drop-line with a carabiner thru the wrist-loop' shown as a DIY for campers traveling in recreational-vehicles.
Half the dogs i know would gnaw thru that leash in 20-minutes, working when nobody was watching them, & be off like a shot...
Nylon-coated cable can't be gnawed thru.
I certainly wouldn't recommend the contraption you mention above for any dog who actually needed to be secured, unless within direct site of the owner. That said, dogs certainly can chew through cable, given time and lack of supervision.
Not unless it's super-cheap 1/4-inch. So much for 'durable' & well-made
Sure, dogs can gnaw off the coating, yes - 3/4-inch twisted metal strands under it, no.
MOST prefab cable tie outs or trolley systems are 1/4" or less diameter cable. The coating probably adds 1/8" to whatever the actual cable diameter is, so many are less than 1/4". Most don't even list a cable diameter on their product, just a "size range". Offhand, I can't even recall ever seeing off the shelf 3/8" cables for dogs. Total diameter for those would be nearing 1/2", and they would be pretty ungainly to manipulate, heavier than most pet owners want, and expensive for the length of time they would last. 3/4" cable would be incredibly stiff if used as a direct tie out, and super heavy for use as a runner (about 1lb/foot). Given that it still wears, corrodes, etc from exposure, probably not worth the extra expenditure when something much smaller will still be more than adequate to secure any dog, as long as you keep them from abusing it. Cable has to be "protected" compared to chain, which is the downside to the light weight. It doesn't like to be dragged, abraded, shock loaded, kinked, or twisted- all of which dogs are likely to do it it if used as a traditional tie out. IMO the only way to make it last is as a trolley off the ground.
FYI- if you sort of gnaw at cable with bolt (or better still, wire) cutters, a few strands at a time, you can make pretty short work of even 3/8" cable. I use it to secure my boat engine, and use several pieces for that reason. You don't need brute strength or leverage, just time.
The vast majority of dogs that i've seen on tie-out trolleys aren't itty-bitty toys, they're typically in the Med-Lg range of 40 to 60#. // 1/4-inch cable, to secure a dog of that size, would look like string.
Most tie out trolleys (including the ones you showed) use cable SMALLER than 1/4" in diameter (though they DO look like string! I believe the ones you chowed are probably closer to 1/8"). That said, most 1/4" cable has a breaking strength greater than 5,000lbs, so it's still stronger than any of the hardware on it!
I asked where you find 3/4" dog tie out?
You can get larger cable (also called wire rope) online, or through industrial/some hardware shops. Most of them will cut it to length and even splice/sleeve eyes or hardware in for you, though I would imagine some might charge for the service. I would recommend asking the merchant's advice on which size/type is best for your given project, as they may be able to recommend a specific type/size over others depending on what traits you need (flexibility, weight, durability).
