Having played one, I found the Binder filled kind of a similar niche to the 3.5 Bard. Eg, if your party needed a specific role filled, there was generally a better class than Bard to fill it, but as a wildcard / backup / second-best-in-slot, the Binder worked great, especially if you knew what you were getting into ahead of time. Did it have problems? Yeah, a lot of the classes in 3.5 did, from the PHB straight to the final released book. But goddamn was it fun.
We did something similar with having the first time binding of a vestige be the fully roleplayed out scene, with future bindings being short interludes mostly handled in the same way that the cleric described praying for their spells in the morning, but with the added fun of occasionally going "sorry guys, I got horns and can't lie today." Which is not sarcasm, having those wildcards thrown into the mix was one of my favourite parts of playing that class.
Man, now I want to go reread those books. Binder and Totemist weren't just some of my favourite classes in D&D 3.5, they were probably two of my favourite classes in any class-based ttrpg.