Yes, as Kraken said, this is not a unit that will generally make back its points through killing enemy units/characters (unless, as mentioned, your opponent is dense). The single digit increase in BS makes blowpipes much more effective, as they can move and double shoot at longe range targets and still benefit from poison. That said, you're not going to wipe out entire units with Chamo skink fire.
That said, their benefit comes through their ability to march block entire flanks of an enemy army through their enhanced scouting ability. The added -1 modifier translates into your opponent having to dedicate magic or a combat unit if they wish to root them out.
But for all of this, Chamo skinks suffer from the fact that they are a special unit. Competing with three units that play an integral role in many armies, it becomes difficult to justify using a special slot for one small tactical unit. Terradons can march block more effectively than Chamo skinks, and at the same time can charge warmachines and fire support units that Chamo skinks are forced to hide from. And if one really compares Chamo skinks to standard skinks, 10 Chamo skinks cost the same as two 10 strong units of standard skinks w/scout and a brave.
