All the Vltor extensions I have received are 5 position, even from way back when it was a relatively little known company in 2003.
The only 4 position tube I have is from Colt.
I don't see the benefit (only drawbacks) of going with a non-spec extension. Colt, Vltor, LMT, and Magpul all produce stocks that conform to specs. Magpul will make a "commercial" (read: non-spec) tube for its CTR stock, but if you want to future proof your investment in the buffer extension, so to speak, the bet is on milspec extensions, all serious stock makers have military applications in mind, if you want to be compatible with future development in carbine stocks, buy once and do it right and get the milspec tubes!