Today's joint came out better, but had a tragic flaw: one of the half-tails broke off during assembly. A good lesson.
I used a coping saw to remove most of the socket waste this time. Much faster, as expected. I also carefully sharpened all of the bench chisels, which didn't seem to need it, but of course worked much better after this process.
I'll do at least one more using this same alder board (still getting a feel for its chippy nature) but then probably switch to some other types of wood. This joint took less than half the time of the first one, and has a much tighter, though still flawed, fit. Learning lots and having fun!
Sockets after clearing waste with the coping saw
The curved hump on the top is where the half-tail popped off. In a real piece, it could be glued.