As stated above, they work well so long as you're pressure bleeding, not vacuum or gravity bleeding. With that said, the thread sealant does need to be refreshed every so often so that you don't pull air around the threads, but you can get a bottle of it for less than $10 or $12 last I checked and for most applications, it will take years to get to that point given how rarely most brakes are typically bleed or flushed.