Bone devils are supposedly somewhere between barbed and bearded devils in terms of power, with 10 RHD. They're large (finally!) but their stats leave a bit to be desired: even the medium-sized barbed devil has better strength.
They're also the first devils I review to have a fear aura. While I'm not too sure about its actual strength (fear immunity is a thing), it doesn't require an action and may just win you an encounter.
A bone devil's poison is... not that great. Monsters with high strength won't notice the damage and will have high saving throws, while the poison isn't strong enough to paralyze monsters with low strength outright. And that's before going into the hordes of poison-immune monsters that start appearing at these levels.
Finally, the spell-likes: Greater Teleport is par for the course. Dimensional Anchor is something every party should have access to, and it may as well be you. Fly is at-will, so it'll give you and your party limitless flight all day (just watch out for dispels). Wall of Ice, too, is highly useful, especial. Invisibility and Major Image, especially the former, have lost some steam by now, though.
The devil-summoning is typical for a fiend of this level. Reasonable chance to get a bunch of near-worthless lemures, smaller chance to get an actually useful bone devil.
Compared to the Vrock, an evil outsider with equal RHD and CR, bone devils have slightly worse stats, worse speed (though Fly turns this around), somewhat better natural attacks (assuming they are not using their claws), a bit worse summoning, about equal special abilities and better SLA's. I'd argue the two should have the same ECL, which would put the bone devil at +1.
+1 for now, feedback is welcome.