Yup, what Remon said, with one minor correction/clarification:
When they believe they have enough stable fixes/features they compile a big patch and release it to the public.
To be clear, Dev branch is also open to anyone who owns the game. It just comes with the caveat that it might not be as stable as the regular branch.
That said, re the helos: I only had about 20 min so far to try them out, but do note that as of last night, in order to bypass licensing issues*, you'll need to use the mission create to place one of the helos with "player as pilot", versus placing them empty on the map and entering from on foot. Note you'll still have a little window on the right hand side of the screen with the option to "purchase".
*This isn't a legal issue or anything, as I believe this still only works if you've got the founders package or the DLC bundle (I own the latter). Rather, the problem appears to be the way Steam recognizes ownership of the DLC. The devs clearly stated in the dev branch change log that there might be issues here, and they're working to resolve them. No bigge
BTW: Dev branch also has an early implementation of VRS active on the Little bird and Mohawk helis. It's pretty rough at the moment, and the devs stated it might get pulled from the initial public release of the DLC, as they continue to polish this feature.
Some other highlights:
-New GUI for gauges (see second shot)
-New UI for Sling loading (not shown)
-Rear door of Huaran (chinook) can be raised/lowered by pilot. Not sure how this plays into on/off loading of troops or cargo yet.
-Both Helis can lift the Humvee type thingys (forget what they're all called in game, but it's basically the futuristic humvee equivialnt)
