Brake and clutch fluid moisture tester

I'm looking for advice about an auto diagnostic tool that's new to me.

Most of us bleed the brake and clutch hydraulics every 2-3 years to make sure the fluid doesn't absorb so much moisture it starts corroding components.

Does anybody have experience using a brake fluid test tool like this one or this one to measure the fluid moisture concentration on their D or any other car? If the reading is correct for all of the fluid in each system and if the 2-3%(?) max limit is is correct then an owner would get a better idea about when to flush-fill each system rather than doing it by the calendar.

Some of these testers run $12-35 at auto part stores and online. Snap-On doesn't show them in stock. MATCO does. At $65.

Any folks out there who use such a tester and can share a recommendation?

I'll keep bleeding fluid by the calendar until I trust a better method/tool. A long trail of false test readings would be expensive.

It would be interesting to see how fast fluid absorbs moisture. Our reservoirs have an air bleed hole so not sure how fast that small hole affects moisture. I would think after a long drive the fluid gets hot so when it cools it sucks air into the reservoir.