A biocular lets you use both eyes to view from a distance of a foot or more. This is great for long viewing sessions, such as an all night surveillance where you would get tired holding the piece up to your eye for any length of time. The biocular, especially the larger ones, also are very useful for driving at night or piloting a boat through dark, maybe hazardous, waters. The biocular is also used where several officers must observe through the night vision at the same time. Try it, you'll like it.
Several mounts are available for night vision systems.
If you do opt for a tripod, spring for a good one. For handheld use you don't really need any mount, but a pistol grip is an inexpensive accessory that makes life more pleasant. A pistol grip threads on and off the tripod mount in seconds. For the night vision scopes that are equipped with a spot illuminator, you can get a pistol grip with a trigger switch that will control the illuminator. Other innovative accessory mounts include a car window mount that clamps down onto a side window in your vehicle and supports the intensifier.