Created by Don Lindich, this keeps track of stylus hours.
I keep a notebook and write down the date and the elapsed time of listening to discs as well as to vinyl. This pretty well tells me how much time I have on my cartridge and also tells me how many hours I have on which tubes.
I tried that for a while. Turned out the total elapsed time I was able to tolerate listening to discs was zero. So now I just play records. When they sound good I play more. But they always sound good.

On an Index card I make a Roman numeral mark for every album side. 20 minutes per sid. Total divided by 3 is the hours. Not exact. But its closer than the hrs shown on my lawn tractor. I forgot to turn off ignition and it now shows 60-70 more hrs than actual. Same would happen with this timer. Forget to stop and I bet your time is messed up (fubar)
An example   iiii/ iiii/ iiii/ =15 sides or 5 hrs 

The shipping on one of those was $12. With tax, shipping etc, $16.08. Not much less than the OP's link
Uh....the Stylus timer is fine. The sample deal has expired! Just couldn't help but goof on another audio gadget.
And yet nobody, even the manufacturers, can say how many hours a stylus can play before it needs replacement.  

Maybe just listen for a degradation of image and soundstage.  Maybe depth of image and layering.  Those are indications that the stylus is worn and needs to be evaluated by a professional or replaced.  
Don't you all just wait until the tonearm simply skates across the record?

Have I been going at it wrong all this time!

I use an app on my phone called Tally.  You can have separate counters for each cartridge.
Repacked made in China...not that it’s a bad thing
Don whoever just beat me to the punch”

Hi there, I am the guy who designed the StylusTimer product and brought it to market. What you linked is just a simple kitchen timer that only does minutes and seconds. I started with that shell to keep costs down, but the guts and the display are completely different and unique to my product, which I own the rights to and is not available anywhere else. My design only records hours, it tells you when it is operating, it remembers the hours when you change the battery, and you have to hold the reset button down for over three seconds to reset it, so you don’t reset it by brushing the reset button or pushing it accidentally.

Put it to the left side of your turntable and push start and stop with your left hand as you operate the cuing lever with your right. Do this a few times and you will never forget as it becomes second nature. It would be nice to automate it, but that would add a lot of expense and could change the aesthetics of the turntable. Mine does take a little bit of user interaction, but playing records is inherently a manual process anyway. If you try the two handed method I described above, you will find it really isn’t that difficult. I have pictures on the website as well.

My StylusTimer may not be for everyone, but it’s under $20 delivered and with it you will know exactly how many hours are on your stylus, track break in time, observe changes in sound quality precisely over time, estimate stylus replacement, etc. You will also see exactly how many hours you spend enjoying music, and seeing that number grow is actually a lot of fun, at least it is for me.

I am a vinyl lover like the rest of you and to those of you who purchase it, thank you and I hope you enjoy it!