In 7th ed, you could run a steg with the unit for stubborn and the skinks and rules protected the Krox from being targetted by shooting and in combat and made the unit very effective and somewhat points efficient both in protecting the steg and the unit. They took away the ability to run the skrox unit with the steg and then took away the ability to protect the Krox from being targetted in combat such that, even given the Krox +1S and giving skinks +1AS it is harder to justify now.
The initial post kind of hit the nail on the head. The ability to target the Krox means opponents will choose how to optimatlly attack the unit for max effectiveness. They will go for skinks to max combat resolution (ACR) and cut down ranks (SCR) but will go after Krox first to reduce the attacks back when heavily armoured or high T and fearing little from skinks. Thus, your opponent gets to choose how to target in combat the models in your unit. That being said, remember that the base contact rule reads such that supporting attacks on the opposing unit cannot target the Krox and that should allow some Krox to survive to hit back in most cases.
On a wounds basis, the allocating of shooting type attacks to Krox is slightly disproportionate to the Korx unit in that you have 8 wounds of skinks for each 3 wounds of Krox and the allocation is based on 8 to skinks and 4 to krox.
I think of Krox like maneasters in the Ogres army; they can hit really hard but at T4 and 4+ AS they are just not quite tough enough and armoured enough to justify the premium points cost for the +1S and great weapon options except in certain battles, like against high Armour save or high T units but that have lower WS, attacks or S units or that strike last. (Maneasters are actually even less points efficient adue to their poorer armour save and greater effective points cost, even when one can customize models in the unit to max the great weapon attacks back.) Basically, Krox have +1S and +1AS relative to Ironguts and better effective LD than ironguts and cost a bit more as a result, but don't have the Ogre charge and magic banner options of ironguts, nor are core options without taking skinks. Thus, with the lower points costs per Krox and +1S they got in the new army book, Krox are fairly costed relative to Ogres given their +1S and LD7 cold blooded but probably better now as a special unit used for flanking. flank protection, and dealing with really tough and high armour save units where enough survive getting hit and wounded first to hit back really hard.
One role for skrox that I think is under-rated is that of using a single Krox with 10 skinks in a 6 wide unit (6 skinks in front and 1 Krox and 4 skinks in second rank) or even 2 Krox with 16 skinks. The reduction of the LD of skinks is an issue if units flee through each other or have to take panic tests outside of the range of the general and BSB and for purposes of rallying. The benefit of the LD7 cold blooded (over LD5 cold blooded) really enhances the ability of this unit to avoid failing terror checks, fear checks and panic tests when away from the general and BSB and it increases the likelihood that, when charged, the unit will survive and remain steadfast for a turn against things like WoC chariots and monsters (if they don't get off a breath weapon). Also, have to split attacks means often over-targetting the Krox which allows more skinks to survive. Splashing one or two of these units in an army and running those units out wide to cover and protect flanks and act as a flanking unit can be quite effective. Plus opponents will sometimes devote excess resources on that unit to the benefit of more important winning units in the army.
The other role is as a very deep and ranked skrox unit to protect the special character Tetto, especially when run without a slann to give the unit some defensive punch and increase the steadast staying power of the unit. With Tetto, you can usually get off heavens spells to reduce the hit rate on Krox and increase their effectiveness in combat.
In certain battles, one might face things like steam tanks and terrorgheists and heavy core cav (like empire and Bretts) where the extra movement and range and hitting power of the Krox can be quite effective, especially in the flank. Steam tanks are eseentially big roadblocks and semi-mobile cannons. Charging one with a couple of Krox in a skrox unit means a good chance of getting a couple of wounds or more on the thing the first round (also avoids impact hits from the thing) and both Krox will survive to the second round of combat and likely survive whatever the steam tank can do to hit the tank against and put more wounds on it. Getting even a couple of wounds on a steam tank reduces the effectiveness of the tank (increases the probability of steam mishap roll and the tank not being able to do something or do as much as the empire player would like and prevents it from moving and changing position for a turn to shoort a steg or something.) by reducing the number of steam points the player can risk and increasing the chance of a steam mishap resulting in a loss of ability to do something planned. The scar vet on cold one with great weapon is often more effective and survives a lot longer in combat. but is more ulnerable to being killed outright by empire cannons and the grinding attacks from a steam tank directly hit and can kill a scar vet more easily than the Krox in the second rank (with most hits on the skinks).
Saw the post above, there is a place for a modest investment in a skrox unit instead of saurus and then invest the remaing points in a lot of skink chaff units given that saurus core are probably a point overcosted right now due to their low linitiative making them vulnerable to certain spells.
