As usual, we have a wealth of information and varied opinions here.
I have used Attach-EZ since it was introduced, and I believe it is a very useful tool. However, using it requires a bit of practice, and like all other framing tools, it has limitations.
The best application IMHO is for mounting athletic jerseys and other open-weave garments. I have always fitted such items with a carefully-trimmed, 4-ply alphacellulose board filler to give the garment support, and still do that with Attach-EZ. It not only looks better, but provides better support for the fabric and makes mounting a breeze.
With the filler board in place, I insert the tool from the back of the 4-ply mount board, through a seam in the back of the garment and through the filler board, but not through the front of the garment. It takes about 6-10 of the inserts to support the filler board, which supports the garment. After mounting the garment I add a reinforcing board to add stiffness and prevent warping/cockling.
The Attach-EZ nylon inserts are chemically stable and will not not offgas or react inside the frame in normal circumstances. Nylon will deteriorate from light exposure over time, but if there's enough light to weaken the fastenings to the point of failure, the items framed would also probably deteriorate. I try to hide the inserts under the top layer of fabric, so few, if any, are visible or exposed to light.
My other favorite use for Attach-EZ is to stretch new cross stitch on typical canvas. For fine-woven fabrics or old, fragile fabrics, this is not an appropriate tool.
On Aida cloth and similar sturdy canvas, the weave may be easily separated enough to accommodate the Attach-EZ needle without cutting its threads. And once inserted, the nylon inserts' "H" shape distributes the stress of mounting over several threads of the weave -- not just one thread of the weave, as when a thread is laced through.
My method is faster than pinning or lacing, and for strong, coarsely-woven fabrics, has all the benefits of lacing. Here's how it works:
1. Carefully place inserts all around the perimeter of the canvas, no more than 1" apart and at least 1/2" in from the edges.
2. Place the work face down on a clean-covered worktable and position the prepared mount board (8-ply with sanded edges) face down on it.
3. Beginning in one corner, use limited-strength thread (such as cotton) to lace across the back horizontally and then vertically, similar to a typical lacing pattern. However, instead of lacing through the canvas using a needle, just loop the thread around each of the nylon inserts, similar to the way speed-laces on boots work. This can be done very quickly, with a bit of practice.
4. After speed-lacing in both directions, pull the threads to slightly tension the mount, just as you would when lacing, and tie off the ends. The threads are the "weak link" in the assembly, and would break in the event of excess stress.