If you need some extra leverage this is the product for you. I would think these levers are nearly impossible to snap. Nice handle area, nice build quality, and have a great tip on the end to get under the tire without damaging the tube.
I had the blue handled set already but really wanted this set.? I finally ordered! They are built like tanks, have precision tooling and all of these fit nicely into the hex bolts on the bikes I work on. Took a few uses to get the spinning technique mastered. I love this set, infact I loved them so much I bought the torx spinning set!
I work on my bikes frequently and I wanted to fill in some gaps and replace a few things. The overall quality of the tools is good with some variability. For example, the hex wrenches are only OK and it didn't come with any t-handle wrenches or torque wrenches (which would increase the price). I tallied up the list prices of the tools at about $400 so it's a great value if you are starting from scratch. If you've already got a collection of tools, you would need to evaluate whether this kit is worth it.
I have used Park Tools' GSC-1 Gearclean brush for years, and it does a good job on chains, chainrings and cassettes. The GSC-4 is more specific to the cassette - it's wider, and the bristles are angled and contoured for that single purpose, so it's more efficient for that purpose.
I did have to figure out the best way to use it. The angle makes it "one-way" (hold in your right hand while standing behind the wheel). If the wheel is off the bike, it will only work on the push. On the pull, the cassette will simply spin. And I do prefer to use it with the wheel off, since otherwise the chain is in the way. Bottom line - if your cassette is dirty, this brush together with the right cleaner/degreaser will quickly get it clean.