I've used Cascamite extensively over the years especially where an extended open time is advantageous. It's true that it cures to a had and brittle state but it is very strong. The hardness does become a consideration in a continuous industrial production situation where resharpening costs may be significant. It does need a bit more attention as compared with PVA, ie, mixing and clean-up (best done asap with wet cloth). As for mixing, follow the instructions for your first few mixes but the propotions are not that critical and you'll soon get the feel for what is satisfactory.
Cascamite does have a shelf life, but it is determined by the rate of atmospheric moisture ingress. It's true that moisture can pass through plastic containers, so to keep it usable almost indefinitely I transfered it asap into glass jam jars. I used to buy 1.5kg Everbuild tubs.
For many years its reputation plummeted as manufacturers played around with its formula (its been discussed many times here on UKW). However a couple of years ago the name was bought by a company called UREKA(the name that sticks) and they have gone back to the original formula and have promoted it extensively - I got my free 125g tub, along with many others here, and it works fine.
Regarding H&S, I've never had a problem, Ureka do put all the usual advice on their packaging.
So my advice is to buy a small quantity and try it out.
Brian