The ZFC guy uses the KMC digital chain checkers, which are really just dedicated digital calipers with "prongs" that fit in chains (not 13 speed chains, btw) and have a spring to apply tension. Since this is a 2-prong system and zeroing is done when off the chain, it will incorporate roller to bushing wear into the measurement, and so you may be replacing your chain somewhat prematurely. It's also worth noting that while the display is in 0.01mm increments, the claimed accuracy is only to 0.02mm - which I believe means it could be off by 0.01mm in either direction. I also wonder about the zeroing process, which seems to rely on internal construction accuracy, and not like a normal caliper which you can zero by having the two prongs touch.
There are apparently two models - and I think KMC updated the checker to be somewhat larger, so that previously 0.4mm was equivalent 0.5% wear, it's now 0.6mm that's equivalent to 0.5% wear. Even at 0.6mm, that's still only 60 steps between no wear and ZFC's "100% wear," so take his partial percentage readings with caution on regards to the precision. Even Adam at XFC groups similarly performed lubes together, calling his tests "a blunt instrument."
Also, since I run an SRAM Eagle (GX groupset, X01 chain) drivetrain, I was a bit worried about chain checker/measurement compatibility. Turns out that only the Flat-top chains from SRAM use larger rollers, and so none of the two-prong only checkers measure those properly. However, the 3-prong checkers, by measuring from the same side of the rollers at both ends, do measure accurately for all chains. Pedro's makes an affordable 3-prong checker:
Which is certified by SRAM as compatible with all their chains.
I also think the Shimano TL-CN42 checker, with its split right prong, is also essentially a 3-prong checker and will be accurate with all chains as well.
In general, I think the 3-prong checkers are going to be superior to the 2-prong checkers in just about every way, even the fancy/expensive KMC 2-prong digital chain checker. You can use digital calipers as described in the first post in this thread to zero out the roller wear, and thus act like a 3-prong checker.
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Finally - and this was/is a big revelation - SRAM says that their Eagle and Flat-Top drivetrains are
fine with up to 0.8% chain stretch! Here's a couple of links:
Note that SRAM says their 10/11 speed road chains should be replaced earlier.
To me, this means that instead of replacing at 0.5% measured wear, I can safely go to 0.75% measured wear. And with the Eagle X01 chains being the longest lasting anyway, with proper lubrication/cleaning I expect to get a lot of miles on my chains.
BTW, I've heard reports that some chains from Amazon are fake, especially Shimanos. So, be careful what you order - might be best to ensure it's being shipped from a approved retailer.
