I've got my Navy K-507 for some time now and despite the initial issue with it (ballbearing missing) i like it very much, mostly because of the design, speed and smoothness of the blade deployment.
However, the knife has a few construction flaws, in my opinion!
It has a too thin handle and you can't take it apart.
The stop blade pin has a flat head that makes it impossible to disassemble.
Nevertheless it is a great knife for the money
A few days ago i bought another Navy K-507 but this one's different!
Take a look:
The thing that immediately stands out is the stone wash finish on the blade and handle!
It's very nicely done on the blade but on the handle is ok

The blade is also a little bit different.
Both are razor sharp but the new model has it's name on the grind and, as you can see, it has a more rounded shape on top.
The blade is also thicker as is the handle wich makes it a little heavier.
The jimping on the older version is better though!
The lockup is very solid on both but the newer model has a thicker lock bar with some jimping on it wich makes it more comfortable to grip hard and also to close the knife.
Another great improvement is that this one can be completely disassemblied!
Instead of the flat head screw they had on the stop pin now it has a normal torx screw.
I can already imagine the mods
It's also built it with phosphor bronze washers!!!
That's very nice but doens't help the knife deploying any faster!!
Actually, the older model has a smoother mechanism!
Also they changed the G-10.
It's black also but has a nicer feeling!
It's a little more grippy and shiny like the one on the EL-02B.
Overall, i must say that i like the improved version very much!
It seems like the maker payed more attention to the knife and corrected the few flaws the first model had.
If you're looking for a cheap, medium sized locker this one might be it!