Hi Steve,
I've used the timberlinx on 2 projects. One for some big trusses (rafter to bottom chord connection) and one to attach a timber mantle to a fireplace. They worked well but accuracy is real critical. If you miss drill the cross hole, the joint won't pull tight and I can't think of a fix. Your accuracy of the cross hole needs to be within about 1/4" which should be achievable if the hole isn't too deep and starts to wander. Timberlinx now makes a product which is essentially 2 half timberlinx which connect together with a piece of 7/8" redi rod to make a complete link. I would very highly recommend using this product over the regular timberlinx because it gives you the ability to readjust the center to center distance for the cross holes in case your drilling wasn't quite on. It also gives you a more flexibility on designing your joints because you aren't limited to the standard timberlinx lengths.
One application where I see Timberlinx being real slick (though I haven't tried it yet) is for anchoring a post where you need a hidden anchorage (ie: post is exposed on all sides). Basically you just set or epoxy the 7/8" redi rod in the concrete and screw on one of the half linx. Drill an end hole and one cross hole in the bottom of the post and set the post over the anchor. I think it is a cheaper and more elegant solution than a hidden knife plate.
So much for my free commercial for timber linx. All in all, I think there a good product for certain applications. Particularly, when you have an overly conservative engineer on the project would needs to have steel or when the tensile loads exceed the limits of a regular mortise and tenon joint. I think the tensile loads on the truss job we did were around 5000lbs which are starting to get out of the relm for a mortise and tenon joint.
By the way, the 'half' linx is called an A475.
