http://www.wichard.com/menu-Shackles-0202060000000000-ME.html are their general use shackles. The main halyards recommended are either captive pin or screw pin: http://www.wichard.com/fiche-A%7CWICHARD%7C1494-0202060401000000-ME.html

The one that you cite is for a different condition. If you click on the "More Information" on that other "MX" halyard, you'll see the following:

Applications

As terminal for flying sail furlers:
The MX can effectively replace the terminal of your flying sail furlers, especially the halyard block, by providing an outstanding strength/weight ratio. When luff tension is needed, it can be used:
to replace the halyard block on top swivel
to replace the lower terminal on spool (snap shackle etc.)

As a halyard shackle for mainsail halyards (2:1 purchase):
The MX has been specifically designed to adapt itself to the heads of most mainsails. Thus it can be used in place of a 2:1 purchase on a mainsail halyard making it easier to tension the halyard and hoist the mainsail.

It's not that you can't use the other quick trip spinnaker halyards for a main sheet. Especially with a 2:1 block which reduces the load on the halyard -- it's just that they aren't intended for that. Swivelling, length, reliablity, and cost are probably the reasons that Wichard would cite.

If hose spinnaker halyards were intended for that, more people would use them. Especially racers and "big boats". Wichard would be glad to sell a halyard that costs a lot more too ;^))))

http://www.wichard.com/fiche-A%7CWICHARD%7C1494-0202060401000000-ME.html