1. It's a 3D display that can show game information (i.e. units) in its own rendition of the world, in a separate window which can overlay CMO. In CMO it shows a real-time view of units in the world. The units are not realistically rendered but are faction-coloured 3D models. See enclosed pic.
One caveat - at present there's no Fog of War, though this is a requested feature and the devs have said they'll consider that. WarfareSims site also has detailed map tiles and elevation data which can be added to enhance the world view.
2. Get it from their own website or from Steam. You need the advanced version, though the free demo will work for a month. Another caveat - the Steam version is not standalone. Just now it's in a bundle with CMO - discount still works if you already have CMO on Steam.
3. Yep, 16 gig is fine. The main lookout is that it uses substantial GPU. It does run on the integrated CPUs that I've tried, but GPU stays at 100% there. On a GTX 1080 Ti it's a stroll.
4. Subjective - I'd say yes. I got it out of curiosity, though mindful that it also works with some flight sims I use. I find it mostly useful as a learning tool - better visualising what's happening in 3D, though I don't often use it when I'm playing CMO 'for real'. As CMO has an endless learning curve, I reckon I'll always find a use for it.
5. In the Options panel, there's a tab to point to the Tacview executable. Thereafter launch it from View->3D View. BTW run Tacview once (to initialise) before using it in CMO.
6. Yes, but not Armored Brigade AFAIK. It works with DCS, P3D and BMS Falcon4, although I've not yet tried it outside CMO. Maybe time for a request on the ArmBrig forum...