Thank you both. So a couple of thoughts:

1. Glyph of Warding doesn't seem available on the warlock spell list right?

2. Re Summoning and Control, I had considered that, and thought the Planar Binding binding the creature to serve you for the duration would override the summon control, especially since the original duration on the Summon would expire if not for Planar Binding.

3. I did think the Summon duration being exactly the Planar Binding casting was wonky, but something that appears to be sort of hand-waived.

4. Without Glyph of Warding, seems like there wouldn't be a lot of control over this as if you could choose your Summoning spell, and the creature you summon, each day. Given that warlocks can't upcast this, it will never be for more than 24hrs, so seems like more trouble than it's worth to catch in the wild, so to speak.