I switched to tubeless tires about nine months ago, when I upgraded the wheels on my bike. These stems work great and installing them was very easy. I've had absolutely no problems with them and they appear to be well made. It's also convenient to have one of the caps function as a value-stem removal tool.
Adding new or additional sealant is easy with these stems. Just take out the value stem using the valve cap that functions as a removal too. Then inject the desired amount or sealant, and re-install the stem. I use a Park Tool sealant injector for injecting the sealant.
If there's any downside to these stems, it's that they are a bit expensive.
I wash and clean my bikes a few times a month. When I use this spray degreaser along with the Muc-off bike wash my drivetrain always looks brand new. It performs way better than expected.
I use these whenever doing a full cleaning. Each pliable waterproof disc separates into two sheets. The inside one has a cutout to place between spokes and disc. The outside one has connecting velcro-like matching connector to the inner. Just mold around front fork and the rear around the stays. Keeps the brake discs protected from cleaning products that will make the braking squeak. Just remove and a little cleanup under and hang the covers or dry overnight. I've probably used on 25 cleanings now and I would purchase again.