I have used the Langka kit, (Also sold under the Mother's label), with mixed results.
Fortunately, I haven't had to deal with large areas, just the occasional rock chip.
I used it with touchup paint from the dealer and I have no idea who actually supplies them.
Quite few application tools are available and while I like the camel hair artist brushes, they are difficult for me to keep usable. I have pretty much settled on what is almost a miniature "Q" Tip made by Microbrush and can be purchased at some auto body supply stores. The best thing about them is that they are cheap enough to use and throw away.

One good thing about the Langka, you can remove all the touchup paint without messing up the vehicle paint. If you screwup, just remove everything and try again.

One tip that you may already know. The touchup paint will shrink as it dries. It might take a couple of weeks to build up a chip to the level is should be before trying to finish the job. I let each application of touchup paint cure for a week before either adding more or trying to level it.
Like I said, I have had mixed results and have had to do several areas over.
I also use a tool that has fiberglass strands in a pen shaped handle to prep the area I'm working on.