Title says most everything you need to know. I have a brand new in box, never used, never opened RS Reverb Stealth dropper.

380mm length
125mm dropper
31.6mm post diameter
Includes bleed kit (I did not have to bleed mine when I installed, but do make sure you have 250 PSI in the post before you install your saddle)
Includes 2.5wt oil bleed kit for tubing length adjustment, line coupler for routing, instructions, Enduro Collar, and a right or left hand (MMX-compatible) remote handlebar-mount kit with 2000mm of pre-bled tubing.

That as cheap as the cheapest on ebay and you don't have to deal with ebay. $300 is low retail right now it seems, $350 average.