When they first appeared they were bulky and expensive. Three years after Texas Instruments invented the silicon chip, four function calculators (add, subtract, multiply and divide) were introduced as $US100 mass-market items.
They got smaller and smaller and cheaper and cheaper and many new designs were introduced. Casio led the way and became the real pioneers of the calculator world.
Sharp introduced calculators specifically for business and scientific applications. Credit card sized calculators had appeared by the late 70s, with pressure-sensitive pads replacing buttons on a keyboard.
Manufacturers added musical notes to each key, alarm clocks and various other goodies to their new flatter than flat offerings.
There were some nifty games to be played on the calculator and hours (well minutes!) of fun to be had at school by spelling out (preferably rude) words upside down on the calculator.