I often use 2 units of cammo skinks, sometimes even 3. As mentioned they have several roles in the army so they are very versatile and tacticaly flexible. The are great for scouting, shooting and harassing.
Pros:
Scouting: If you scout with them keep them small, 5-6 skinks per unit. This way they are still cheap and expendable and can often scout in a good position unlike big units. As a scouting unit they are good for taking out war machines, I usually spend 1-2 rounds of shooting at the crew until they are reduced to 1 crew member, then charge and kill them. As they have -2 to hit when shooting at them even RBTs will have trouble shooting back. Scouting is a good way of marsh blocking early in the game, especially if you don't have terradons.
Shooting: 6 Cammo skinks costs about the same as 10 regular skinks. As you will often be shooting at long range and while moving the skinks are stuck the regular skirmishing skinks are forced to use single shot (otherwise they hit at 7+ which can score poison hits) while the cammo skinks can move and shoot at longe range and still use their double shots, which means that 6 cammos will often shoot 12 shots vs the skinks 10 shots, so shooting wise they are very similar to regular skinks when it comes to shooting at non-large targets.
Harassing: They might be worse war machine and mage hunters than Terradons, and less mobile, but they are incredibly hard to catch. a unit of 5-6 cammo skinks are amazingly fast and are excellent for frenzy baiting, regular baiting, march blocking and diverting.
Cons:
They take up a special slot, which can be used for terradons, CoC and Stegadons, which are all very solid choices. They add shooting which can be covered by a core unit and harassing which can be covered by terradons (who are much better harassers and hunters). They are also very fragile against non-BS ranged attacks such as the Organ gun, Lifetaker, Anvil of Doom, direct damage spells etc. A unit also have very few wounds, 5-6 wounds on T2 will get wiped out by a single 2D6 S4 spell. Overall they are a good unit due to their felxibility and multiple roles, but their still inferior to some of the other special choices. Not a super competative choice imo.