1. No. The .16 mod is great or if you can find one, you can do like I did and get a JDM STi BPV which comes stock with a terribly soft spring and is supposed to hold 20-25 PSI or thereabouts.
2. They are basically the same. A two stage one just has the vent pressure at a fixed level. With an adjustable, you can custom "tune" the BOV to vent at a certain pressure.