What is Reddit's opinion of Sparco Tally Counter with Finger Ring, Silver (SPR24100)?

From 3.5 billion Reddit comments

I knew they were counting because my whole routine would be

• Fish out card from the wallet, holding it up as I walked by

• Get The Nod from the door person, and hear a little click as they trigger the little counter.

Didn't know they were using it to adjust the registers though, that's smart.

Do they keep track of people leaving too?

No, the border guards are fully equipped with clickers

Here is the desktop version of your link

Which counters? Are you talking about the digital ones? It's just a calculator.

There's stuff like these: http://www.amazon.com/Richards-Company-Counter-Finger-SPR24100/dp/B0008GOGI8/ref=sr_1_3?ie=UTF8&qid=1457999673&sr=8-3&keywords=counters

or just small tokens

http://www.amazon.com/Learning-Resources-Transparent-Color-Counting/dp/B00004WKPM/ref=sr_1_5?ie=UTF8&qid=1457999673&sr=8-5&keywords=counters