This particular kit is the hand phaser from TOS, mastered by John Long. He goes by the name JLong online, by the way. John has been building and offering some really great Trek kits over the years, and each iteration shows marked improvements over the last. I cannot say for sure where this kit fits into the evolutions of his offerings, but I do know it's highly sought after, and very accurate.
Included with it are metal upgrade parts. I have a machined aluminum nozzle, a dilithium chamber cover by PhasersOnStun, and I think the wheel from the back is an upgraded part too. The mesh was also not standard with the original kit offering, IIRC.