It's pretty obvious that my Horizontal Router Mortiser (HRM) cuts mortises for use with loose tenons. It does that job very efficiently on anything that can be brought to the machine. And it does it part after part without having to layout the mortise on the parts. You do that on the first part and never again until you move on to a new size mortise. Some typical matching 1/4" mortises in two parts to be joined with a loose tenon.
Slip in a loose tenon, which you can make any size from project scrap, and it's ready to glue up. And on the ends of rails, it's easier to clamp the workpiece on the HRM than to try to hold a Domino up to it. Also, once the workpiece is clamped to the HRM sliding table, making the cut is safe and requires no holding/plunging of a router like on many router mortisers. When you need to do dozens of parts lifting and guiding a router is a tiring and potentially dangerous undertaking.
I see no advantage over loose tensons, but if you want to cut integral tenons, the HRM is well suited for that task, too.
Whether cutting mortises for loose tenons, or mortise and integral tenon joints, the HRM gives you clean, parallel cuts, with no paring or clean up required for a precise fit of the tenon.
I'm happy to sell you a HRM, but you can build one for not much money and a day or two of your time from the SketchUp model at the bottom of
this page on my website. If you don't use SketchUp, I can send you PDF files for the major parts.
John