In my experience, the poor Melee and dreadful defence of Ghekkotah keeps them from being good as anything except a not-particularly cheap distraction/objective runner. The large number of attacks means they can make an impact against soft targets, but they bounce right off anything with a decent defence, and a hindered charge penalty sidelines them completely. Defensively, the combination of defence 3+ *and* a dreadful nerve of 12/14 for a regiment means they are beyond simply fragile-any attack, however small, is a serious threat. Overall, they are a support unit, not a serious fighter, and that means they only do well when they have stronger units to support.
I only use them as chaff, and only in troop size to keep them as cheap as possible. If they get a flank they can do some damage, but at 70 points I don't expect them to. I am generally not concerned with unlocks, as I tend to bring enough hordes of Primes, Fire Elementals and (occasionally) Ancients on Rhinosaurs. If unlocks are a problem then I guess paying an extra 30 point to bring the Ghekkotah up to regiment size wouldn't be that bad. I would not, however, try to go MSU with the Salamander army.
Once their attacks are bumped to 40 a horde of ghekkos with hammer of immesurable force is something i want to try. 40 attacks hitting on 5's and wounding on 4's rerolling 1's is not bad
maths out to around 13 hits and 8 wounds regardless of what def you are going against. thats a good can opener
I use Ghekkotah in two sizes, troops as chaff and flankers (maybe even objective grabbers) and a Horde with the hammer for some VERY reliable damage output against anything. But using them as MSU? Not sure, it might work but it's not my style