I use HP calculators every day. 12C for most common tasks, 25 in the workshop (it can be operated one-handed!), 15C or 50G for more complex tasks involving units.

Calculators are very useful, using them is a forgotten art. While it no longer makes sense to plot anything on a calculator (I use Mathematica for that), it is still a great tool.

I have a 16C and I use it, but only when developing embedded software where I need to wiggle bits. It is very useful for that, especially with one-key switching between bases (HEX/BIN/DEC).