Not interested in a urinating match here.
Just some clarification of what I said before. You use rope on your suspension. Fine. Your business, your call, your customers. You have a model of how to hang and have made a device for it. There are other models. A common belief around HF is that for a variety of reasons it is good to use webbing around the tree, even if the rest of the suspension is rope of any kind. A goodly number of camping hammock makers make the suspension from webbing.Clark. Claytor. Warbonnet. Jacks 'R Better. Tree-to-Tree. Your hook can be used if people want when they have tree straps, but not solely with what you provide. Some cord and some other device (which might be as simple as a toggle for a marlin spike hitch) would be used.
Your price of $12.50 shipped for a pair of hooks is a good one, considering you're in the Netherlands. A price of $7 for one Camp Nano biner is also a good one, a pair then for $14. The difference---shipping. If someone wants to pay as much as you cite for shipping two devices, well it's a free country. But it is a well known phenomena that you can amortize shipping costs when you have orders with multiple things in them. Some of the sites that offer these biners will also give you free shipping if your order is large enough, usually around $50. It's not hard to make a $50 order of outdoor gear! So that's the way I, and other cost-conscience consumers purchase gear.
Finally in answer to your question, why would I want something stronger than 1000 lbs test weight? This is safe enough in most applications, but there are complicated forces in hammock suspensions, easy ways to multiply them, and peak dynamic loads can be uncomfortably close to 1000 lbs depending on what you're doing in the hammock, e.g., someone heavy dropping into it and there is tightly tensioned structural ridgeline. So for me, at 200 lbs dripping wet on the scale, when it is easy and cheap and lighter to use something that is stronger than 1000 lbs, I will. Hang your own hang, but make sure your health and life insurance premiums are paid up first.