So these aren't perfect, but they're close enough.
After the glue dried, some legs had an open seam. There's a trick to solving this problem.
Step 1: Stare at unsightly open seam with disdain.
Step 2: Take your burnisher (or screwdriver) and start at a shallow angle to one face of the leg. Start rubbing back and forth, applying firm downward pressure.
Step 3: Take another pass at a steeper angle. Gradually push the wood and glue over. Do one side, then the other, then back and forth until the seam closes up.
Step 4: After a light sanding, it's pretty much seamless.
5 lock mitered quadrilinear legs done. Always make 1 extra leg. You never know when you're gonna screw up.
I read one post about a guy beveling the edges of each board before sending them through the router, to minimize the amount of material the bit has to remove. He seemed to suggest that this minimized tearout, though not 100%. His lock miter bit must have a different profile than mine. If I did a 45° bevel it would cut away part of the little tongue.
I don't know if I'll keep using this joint. Maybe I'll start glueing a few boards together to make thicker stock and do a thick veneer to cover the other two faces of the leg.
I'm just glad this part is done. Lock mitered, quadrilinear legs are the least enjoyable part of furniture projects lately. I really hate routers and this has to be the least enjoyable router bit to use.