Some time ago I bought this coin acceptor. Programming it to accept 4 different types of coins is convoluted, but quite ingenious, and works exactly as the spec sheet indicates, without glitches. Surprising for such a complex task, considering that the user interface consists of 3 buttons and two 7-segment LED displays.
After setting it up, the mechanism identifies each coin type reliably, even providing user-friendly feedback (showing on the LED display the number of impulses sent over the COIN/white wire), very helpful for debugging.
Now onto actually using it. Adafruit’s graciously provided the “Piggy bank”sample project, including the Arduino sketch as well. The sketch however, counts the impulses simply in the loop() function. That may work fine in that particular setup, with just the coin acceptor (1 coin type nonetheless) and the LCD display. If you want to add more hardware (printer, buttons, bluetooth, SD card, LEDs etc), you need a smarter, hardware-independent, way to count the impulses from the coin acceptor. Naturally, that involves interrupts.