you nay-sayers seem to arguing around the question. i don't think anyone looking to buy them denies that they are proprietary. that argument seems lacks persuasiveness to me. if you are looking for an alternative to a threaded cog system -- which definitely has its faults in non-velodrome contexts (read: lots of backpressure and skidding) -- then you are going to have to go with something "non standard." new products that enter the market don't automatically achieve "standardized" status, as you might imagine.

the level system is significantly superior to disc bolt-on systems because the stresses are absorbed by the machined "knuckles" rather than the bolts themselves. in the case of level, the bolts only serve to counter the minor lateral stresses that one encounters. this is not to say that disc hub retrofits can't work quite well, but, to me, they are a kludge rather than a well thought out design.

that said, there are some potential downsides to the levels. for one, they are pretty heavy. that's the price you pay for the epic burliness of these things. the level guys do fixed mountain biking, so i imagine that this penalty is well worth the added strength and reliability. i would like to see level design a less epic version of the hubs that still uses the bolt on system but is a little more weight conscious. also, the small end chain line of the levels is 45mm. this'll put the cog out a little past most standard track setups, which usually run between 43-44 on the back end.*

* -- the 42.5 ideal track chainline almost never occurs on the rear end due to varying cog with and hub design.