The MilKit system is great in theory, but not quite so rosy in practice.
As promised, MilKit does help clean up the often-messy process of setting up tubeless tires. With this system, you can simply mount and seat the tire dry, and then just add sealant later through the valve core, all without spilling a single drop. As promised, the syringe needle and proprietary valves also let you extract the sealant later on to see how things are looking in there without having to take everything apart.

A plastic extension on the end of the otherwise standard Presta valve core pierces through the supplemental seal so you can bleed off air as usual — or, at least, that’s how it’s supposed to work.
All of the bits also seem well made, and the valve stems worked in a wide range of rim shapes (although the sole 35mm valve stem length will only work with shallow-profile wheels).
However, the needle is easily clogged if your sealant has gotten old and chunky, and you still have to remove the tire if you need to remove any of those dreaded “Stanimals” you hear rolling around inside the tire casing. The plastic extensions on my valve stem samples also weren’t long enough to fully break the supplemental seal, either, so I wasn’t able to bleed off any air without using the syringe needle on its own, or a smaller Allen wrench.

The included tube and valve lets you inject sealant in through the valve without making a mess.
Finally, the system is awfully pricey for what it is, especially when much of what MilKit offers (save for the fancy valve stem seals) can already be done with the stuff already on the market. Convenience often comes at a cost, but in this case, there doesn’t seem to be enough added convenience to justify the outlay.