Demonic intelligent animal-people-hybrid monsters, which we get one paragraph of information on and no mention in any other WotC supplement ever again. Yeah, that sounds like the fiend folio.
Abrians are 2 HD medium-sized magical beasts. Their ability scores are a fairly bland +2 strength and constitution, +6 dexterity, and -4 intelligence, which sounds about right for something with that many HD. As one would expect, abrians have an excellent base land speed of 50 ft: equal to heavy horses. Their natural weapons are an unremarkable secondary 'kick' (1d8), and a weak primary beak whose excellent critical stats (3x crit, 19-20 range) are made quite pointless by its low base damage (1d3), with neither reliable enough to be a primary attack mode.
Fortunately, what little information we are given about abrians implies they have thumbs. Their arms are described as 'humanoid', they own standard treasure, the game tells us their weak arms impact their carrying capacity, and WotC apparently also considered them playable enough for a +1 level adjustment.
Finally, abrians have a notable Shriek ability. This hits all creatures (unfriendly!) within a 20 ft. range, dazing them for one round on a failed save. An at-will save-or-suck is pretty dang good, but not hitting allies with it may be hard. Still, it seems wise to err on the side of this being at least somewhat useful, if only on the first round of combat.
Considering all this, I think abrians would be fine at +0 LA. They have a reasonable chassis and an interesting special ability, in addition to everything you'd expect a normal PC to have (speech, thumbs). 2 magical beast RHD are a fine price to pay for all that.
However, adding a single HD bumps abrians up to Large size, which probably makes them worth +1 LA. DMs allowing HD-advanced PCs should keep this in mind.