The all plastic ones are intrinsically safe in a potentially flammable environment, they don't require power, they're an education in how most engineering materials in the real world have surprisingly wide tolerances so they are far more than accurate enough for most work, for people who learn graphically/visually they are the logical next educational step after counting on fingers.
They're pretty useful for teaching amateur people how to implement algorithms. Multiple ways to solve problems, some easier than others, some more efficient than others, with immediate rewards of faster higher accuracy.
> The all plastic ones are intrinsically safe in a potentially flammable environment
Never thought of that, and I used to work in an ATEX environment where calculators powered by watch batteries had to be carefully logged and carried across to a "safe" area inside a special (horribly expensive) Peli case.
They're pretty useful for teaching amateur people how to implement algorithms. Multiple ways to solve problems, some easier than others, some more efficient than others, with immediate rewards of faster higher accuracy.