What kind of helmet is in this A-10 video?
The pilot's helmet in the photo is a standard Gentex HGU-55/P fitted with a Thales Aerospace Scorpion Helmet Mounted Cueing System.  Information on the SHMCS is available on the corporate website

http://www.thalesvisionix.com/overview/

As to weight, the display, cableing, and visor add several ounces of extra weight to the helmet.  It's a little heavier and slightly bulkier than a standard visor on a helmet but not by much.  Aircrews have been flying with HMDs now for about ten or so years without any major impediments to their flying abilities.

There has been a weight issue associated with the F-35 HMD and the aircraft's ejection seat which could cause a fatal whiplash injury during ejection with smaller pilots.  This is being remedied with changes to the seat's pneumatic catapult system, drogue chute deployment timing, both controlled by a selector switch prior to flight, and a newer, lighter version of the helmet under development.