You can absolutely check your chain with a simple metal ruler. For me, this tool is worth it, as I have four bicyclists in my household, and a couple of more bikes than that which I regularly maintain. Also, I worked on a lot of extra bikes this summer, helping refurbish them for people, mostly kids in need, and having a gauge that quickly estimated how worn the chain is, and whether the bike could go out that way or needed a new one was a very quick and easy task with this tool.
Great little gadget. Not cutting edge technology - just a simple tool for making it easier to clean your drivetrain. This allows you to clean your chain, rear mech, and chainrings without getting degreaser/cleaner/solvent all over your rear wheel. Works great on traditional quick release hubs as well as thru axles.
This is the de facto standard for chain degreasers. I've used others and they've worked fine as well, but for some reason, I always go back to buying this brand. It gets the job done for sure. I run the chain through the PT chain cleaning tool twice, cleaning the tool out in between runs, and the chain ends up so sparkly clean you could eat off of it.
Park tool PPL-1 grease is amazing, this is the only grease I will use on my Road, Gravel, and Mountain bikes. Compared to other greases this has no stinky smell and works extremely well in extreme weather. It's the right consistency for bearings, pedals, cranks, and head tubes. Won't harm steel, aluminum, titanium, or carbon frames. I highly recommend this product it's worth every penny.