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 had the iredscent version. They worked fine and looked great. After 7 months, I had to remove the valve to replace a spoke. The portion you don't see that is in the hollow section of the carbon rim was so corroded, the threads were almost gone. The parts that you see still look great. In ride in Phoenix, AZ where there isn't a lot of moisture.
Truth be told, I initially only bought these because they were purple and match the purple anodized bits I have on my bike. I was pleasantly surprised that these are actually some of the nicest valve stems I have ever used. They seal up nice, they don't seem to get as mucked up as some of the cheaper ones, and having the different rubber seals for different rim profiles is nice. I'll buy these again in the future...they are worth spending a few extra bucks on!
I started using tubeless road tires this year and I wanted a sharp looking stem for my hot wheels. My goal was to get a clean look on my Bontrager XXX 4's. I went with the 60mm in black, hoping they would not be too short. After experimenting with the different sets of grommets provided, I got the fit I wanted. I have enough length for inflating, and not too long so another squirrel tries to run through and take out the stem. A rubber o-ring, followed by the stylized cinch nut, polishes off the look outside. The core removal tool / stem cap works perfectly and can ride along if one chooses, at a slightly higher profile than the cap provided. Its the Swiss Army knife of valve stems.
I didn't think "premium" valves would matter but these are a worthwhile upgrade. Haven't tested it yet but I think these will be less likely to clog ï¿½ï¿½other valves seem to have more rubber around the opening where the valve meets the rim, and these have more metal exposed. I've noticed on other valves that the sealant can harden around rubber bits.