I own all three but have only used Fifth Edition Foes in play so far.
The stuff in the Book of Lost Spells would be mostly monster/NPC only for me. I might consider allowing a few of the more flavorful low-level spells for PCs, but definitely not the save-or-suck stuff. And I'd use it sparingly for monsters as well. That said, I can imagine some of those spells and abilities making for very cool encounters when saved for Big Bads.
I used a couple of creatures from Fifth Edition Foes in a low level one-shot last spring. Ice drakes and some kind of ice wisps, I think. I really like the flavor text and background on each creature. The ice drakes were actually an RP challenge, rather than combat. Once again, though, watch out for some of the more extreme effects, as some of them could lead to real death spirals for your PCs. Then again, some DMs like the possibility of death spirals.
I have had Tome of Beasts for the shortest time, and it's also the longest, so I've looked at it in the least detail. It's certainly a beautiful book with a great variety of creatures, lovely art, and excellent flavor in the descriptions. I can't comment on the mechanical stats or what to watch for in using them, though.
The stuff in the Book of Lost Spells would be mostly monster/NPC only for me. I might consider allowing a few of the more flavorful low-level spells for PCs, but definitely not the save-or-suck stuff. And I'd use it sparingly for monsters as well. That said, I can imagine some of those spells and abilities making for very cool encounters when saved for Big Bads.
I used a couple of creatures from Fifth Edition Foes in a low level one-shot last spring. Ice drakes and some kind of ice wisps, I think. I really like the flavor text and background on each creature. The ice drakes were actually an RP challenge, rather than combat. Once again, though, watch out for some of the more extreme effects, as some of them could lead to real death spirals for your PCs. Then again, some DMs like the possibility of death spirals.
I have had Tome of Beasts for the shortest time, and it's also the longest, so I've looked at it in the least detail. It's certainly a beautiful book with a great variety of creatures, lovely art, and excellent flavor in the descriptions. I can't comment on the mechanical stats or what to watch for in using them, though.