The FMT can be used just as easily to make matching mortises for floating tenons. The precision of using it is the same whether you make M & T pairs or just Mortises in both pieces and then use floating tenons, made with the table saw and planer to size them. You don't have to make tenons on the ends of your work. When I make pieces with tenons on both ends, I cut the piece to the length needed plus 2X the length of the tenons needed, minus 1/8" for to cut each tenon to be certain that the tenon doesn't bottom out in the blind mortise. When I set the plunge depth of the router I also set it 1/8" less than the mortise depth. The desired length of the finished piece is always correct and each tenon is 1/8" shorter than the depth of the mating mortise. These measurements are easy to attain and if the tenon length is a bit off, the tenon thickness is precisely controlled by the FMT, so the joint fits perfectly anyway.
Leigh is the only woodworking company that I've ever bought tools from that makes jigs that will do exactly what Leigh says they will do, and do it very accurately. Their manuals are written to make things so clear and understandable that if you can read and understand the instructions, the cuts on your work pieces will fit together perfectly.
For the very few occasions when I wanted to make mortises in the middle of wide boards, I have used my plunge router and a straight edge clamp. No tool can handle every possibility, not even the FMT.
Like I said in a previous post. For the very few occasions when I have wanted to cut a mortise or a tenon on the ends of very long boards, I have clamped the FMT to my shop attic floor at the edge of my pull down stairway, so the longer boards could hang down through the stairway opening, then stood on the steps of the stairway, and did the routing on the FMT. Once, when I wanted to do it to even longer boards, I borrowed the use of my neighbor's 2nd floor deck railing, placed FMT on the railing facing toward the yard on top of the 2 X 6 deck railing, and clamped it in place. The 11' long boards hung down past the edge of the deck to about 4' above the ground, and I routed tenons on their ends using the FMT.
For anyone interested in an FMT, you should watch the Leigh FMT Demonstration and Training Videos on YouTube or available on DVD free from Leigh. Watch them several times, so you learn every step of using it.
My FMT has done what I've needed for about 10 years, and I have friends with Festool Dominos and I have used them. To me, they are a heavy duty biscuit joiner and work in much the same way. Yes, they cut the mortise for the domino very well, but the positioning accuracy isn't much, if any, better that you get with a biscuit joiner. After the experience of using their Festool Domino tools, I still like my FMT better for it's amazing placement accuracy over a Domino. Yes, setup is a little slower with the FMT, but there is no comparison when doing multiple closely spaced joints.
To save you searching for them, here are the links to the Leigh FMT Pro M & T jig videos -
Charley