I kept a couple Barnacle Blennies in my 150 with my fat, fully grown Lawnmower Blenny. My Lawnmower paid the smaller blennies no mind, like he does with anything in the tank that's not covered in algae.
The Barnacle Blennies were very cool, sticking their head heads out of their hole and darting out for food. They stayed in view of the front glass the first couple months, but then started moving around. Sometimes, one or both may end up in a hole where I can see them for a few days, but then they would disappear again for up to a month of not seeing them.
This went on for about six months or so until I stopped seeing them anymore. Really great fish, but I wouldn't try them again in anything bigger than maybe a 20g so I can keep a close eye on them.