I’ve had my speedstir from TFT, I think maybe 15 years, still works. The membrane over the left button has worn off, but, still working. I may have to push the button a couple of times to get it to stay on, but, it goes.
Nonrechargeable batteries last me one to two years, even using it for my pool 5 months a year, and for my aquarium testing throughout the year. Using the pill for the stir, don’t have the +. Sometimes it wiggles, but, usually an off/on thing helps.
Haven’t had any problems at all with ink on the grad cylinders, but maybe they used a better ink back then.
Since I use rechargables for electronic candles, computer mouse, and the like, I’ve switched to rechargeables in the stir. Have to recharge every couple months or so, but that’s no big deal at all.
Nonrechargeables are 1.5 v, rechargeables are 1.2 v. That’s why they don’t last as long. But, it still saves buying new batteries periodically.