Look for them to be called other names too like "Z Clips" and such. They aren't a true french cleat, but many companies call them that.
A french cleat is just a piece of wood cut at an angle. One piece is mounted to the wall, and the other slides over it. You can use these to get a VERY flush fit of the frame to the wall and they are cheaper than the Z Clips. Z clips usually make them stick out from the wall a little. Unless you want that for your look/design.
Here is a picture of how a french cleat, made out of a simple and cheap piece of scrap wood, can allow you to mount the frame flush:
The one piece is mounted to the frame, and the other is mounted to the wall. As you set the frame over the piece mounted to the wall, it "hooks" on to it, and the weight pulls it down into place and it won't fall.
I used a french cleat to hang a 95pound Pachinko machine and cabinet to the wall. It can certainly hold a couple of frames, insulation material, and fabric.