Absolutely perfect for getting all the grime out of your cassette and derailleur rollers! Spray with your soap and water solution or bike cleaning product of choice and spin the pedals. The angle on the brush works it's magic and really cleans well. The bristles are stiff an durable. I use a bio based cleaner with this brush that's a little more than just soap but it cleans very well and then easily rinses out. I wish I had this product a while a long time ago. This is FAR better than a tooth brush or other softer brush you might have laying around.
I've got the other Park Tool for cassette cleaning (narrow brush on one end, plastic teeth on the other) and I'd compare two by saying this brush is the toothbrush and the other is the floss. This brush is great for getting a lot of gunk/dirt off the cassette quickly. I've been waxing my chain so I don't get a lot of oily build up on the cassette any longer, but I can accumulate a lot of dust/mud gravel riding. This brush quickly removes a lot of that gunk where it matters, i.e., where the cassette actually touches the chain. The deeper area between the cogs can wait for when I'm doing a major mid-season cleaning.
Have not had to use one yet, came from sew-up background. Though we can use dollar bills or empty gel packages or other expedient items to accomplish a similar task, I feel more comfortable with using these. The adhesive will help to ensure that the item will stay in place while fumbling with remounting tires and tubes. When pressed for time to get back on the road this can be a real help, especially in inclement weather. I feel comfortable on long rides without hauling a spare tire along when I have a few of these on hand. They are much lighter and more compact than carrying a spare tire. They are not prohibitively expensive so I feel they are a good value item to take on rides.
This is the first torque wrench I've owned, so I have nothing to compare against. The torque settings were easy enough to figure out. I was a little disappointed that this wrench didn't have the loud satisfying click of order wrenches I've seen in maintenance videos. It took a little getting used to for me to feel the knock on the handle when the wrench reached it's torque setting. Know that I've torqued down a couple of chainring bolts and stem plates, I feel very comfortable with this tool.