Question about Houston Public and Harris County libraries

Ok, so this is maybe a dumb question, but I've been out of the loop on public libraries since the 80s.

Is there any real differences between the two library systems? A benefit of one over the other?

And if I sign up for one, does that disallow me to sign up for the other, or can I do both?

Doesn't seem like there are any restrictions, or a difference other than physical locations. Right now I'm wanting to go digital of course.

TIA