As I said in the part of my post that you cut out, "The rest were all considered varying levels of "just fine" to "really quite good". "
Well, I think you're wrong on that, but it's completely subjective, so we can't really argue any more than we already have. I guess we've been skirting around an actual list, so for the record, here's what you can summon:
- 2 dryad, CR 1, can talk to plants/animals and cast barkskin, and can each charm some humanoid with a decent save
- 1 seahag. CR 2, has a death glare that's pretty cool, but takes 2 easy saving throws and will kill your party and not the monsters you're fighting
- 8 pixies. CR 1/4, can cast each cast confusion, entangle, fly, polymorph, and sleep, among other really good spells
- 4 satyrs, CR 1/2, have magic resistance but otherwise suck, I'd rather have 8 wolves
- 8 sprites, CR 1/4, can poison at range and tell you alignment of things, but 2 HP and otherwise useless
- 8 blink dogs, CR 1/4, can teleport a short ways and attack, but 8 wolves is still probably better although these have twice the HP
And that's it, folks! There's actually only one other fey in the whole MM, and that's a green hag, CR 3, and they're pretty terrible as well. (The spell conjure celestial is even MORE useless, btw.) For my money the pixies are the only thing worth casting the spell for. You might come up with some niche situations for the dryad, but nothing else really does much of anything, and you'd be better off conjuring animals.
Again, the main issue is the conjure spells themselves: they are all terrible except conjure animal and conjure elemental, and "conjure pixies" - which is too good. Part of this will hopefully get better if more MMs are ever released, but given the current situation at WotC I don't see much happening... maybe ever.
Ultimately, I still like the idea of raising the pixie CR to 1 or 1/2 at a minimum. That gives you 4 (or 8) pixies as a 6th level spell instead of a 4th, which seems more reasonable.