We do like going "further afield" than Tome of Horrors for OGL stuff... but there's an unfortunate pair of reasons why we don't do this often.
1) A lot of OGL stuff is just unfortunately not good.
2) Of the good stuff that remains, an unfortunate amount of it is crippled content; the publishers made the monster stat blocks open from the size category to the end of the combat info; the monster's NAME is not open. This more or less is a dealbreaker for me, since without a name, there's no way to reference the monster and no reason to go with the monster's stats. Frustrating.
Yeah, it's pretty frustrating when the monster name isn't open content... or worse, they only open the stat block... no name or ecology.