Mechanical terminals more expensive than the usual alternative-swages-but they also have many advantages that swages do not.
Mechanical Terminal Pros
They are as strong or stronger than swages.
Theyre reusable; therefore, theyre cheaper in the long run if you own the boat beyond the life of the wire. In the shorter term, mechanical terminals add to boat resale value.
(Note: Often the upper terminal in a rigging setup is a swage, and the lower one is mechanical. The logic here is that corrosion is heavier closer to the deck. First, this is not always true, and second, you still have to throw away and re-purchase that upper swage when its time to replace the gang, instead of reusing the terminals at both ends.)
Mechanical terminals can be disassembled for inspection, inverted, the wire can be shortened, and if needed, the Hi-Mods can be temporarily removed for installing furlers, radar masts, etc., without cutting any length off the wire.
Mechanical terminals are harder to disassemble, but are the least vulnerable to internal corrosion.
When fabricating a new rig, or sometimes even when replacing an old one, exact finished lengths can be imprecise. With swages, you can either test-step the mast, measure the wire, and unstep the mast, or make very careful measurements in multiple planes. But with mechanical terminals or poured sockets, you can step the mast with generous wire lengths, with the upper end rigged in advance, then turn up the lower ends in place. (Note: It is still possible to get lengths wrong.)
Mechanical terminals and sockets are satisfying; you can put together some meaningful structural items using simple hand tools.
Mechanical terminals can be assembled anywhere, which makes them valuable in a jury-rigging situation, or when you just want to re-rig in some far-off harbor.
The rigger can monitor/determine quality control.
Mechanical Terminal Cons
Many would-be assemblers (owners, crew, well-meaning friends) are inexperienced, and might not be-shall we say-appropriately cautious. To make matters worse, assembly instructions can be incomplete or even misleading. This can lead to expensive, frustrating learning experiences. Poured sockets require the highest level of skill, both for installation and disassembly. Hi-Mod terminals are the simplest to work with.
Reusable terminals are heavier than swages. For example, Hi-Mod and Sta-Lok eyes for 5/16-inch wire weigh about 12 ounces, and a poured socket is about 15 ounces, compared to about 9 ounces for a swage.
Specialized end fittings, like stemballs and T-bars, are available only from Norseman. Well, they were available, but Norseman is out of business now. Some dealers might still have stock.