They're a cool concept, but the problem is, they're a solution- an expensive solution- in search of a problem.
Even today, after they've been available for at least half a year now, there's still a great deal of "okay, now what do we DO with it?"
Unlike a video-game battle-map, it can't tell you where the other guys are, which is just about the only feature a player could really use.
For tournament use, the airball fields are small and relatively simple enough that you hardly need an interactive map to get around them- and without any data on the location of your opponents, even map data is essentially useless.
Compass directions are similarly kind of pointless- useful in a large woodsball field or scenario game, but in an airball or other standard constructed field? You guys start at this end, those guys start at that end. Meaning your opponents are generally thataway.
Interfacing with your gun? Cool concept, and the gadget geek in me "squees" a bit over it, but it's not exactly a game-changer. Tank pressure? We already have these things called "gauges" on each and every tank sold. Takes half a second to read it- in fact, it's probably faster to read and interpret a dial/needle type gauge than it is to read and interpret a numerical display. Which is why even today, with some cars coming with a LCD screen in place of the dashboard, it still renders a physical dial-type speedometer, rather than a numerical display.
I can see a round counter being useful- telling you how many shots you have left. But how would that work? You have 45 rounds left in your hopper, then dump a 180-round pod in. That's more than the hopper can hold, so some is spilled. How does the hopper, the gun, or the display know how many balls are in there?
Total shots fired per game? An interesting data point, but who cares? It's not like the player is getting paid per shot, or there's some sort of enforced minimum number of shots you have to fire in a game.
Help you keep track of how many shots you have left? You can already do that by simply knowing how many pods you have left. Unless you're a pumper or stock-classer, knowing the exact number of shots you have left is unnecessary- no tourney player is going to look at the display and say "Only 355 shots? But I'll need at least 370 to finish this game!"
The HUD system was originally developed for snow skiiers, so you could have an interactive map of trails or the route down the hill. That actually has some use. Similarly, I could see a map of a big scenario field (the Oklahoma D-Day field is 600 acres!) with things like established 'enemy' encampments, 'medical' stations and other objectives clearly marked.
But for the average player, on a typical constructed paintball field- which is typically only an acre or two, and fairly open? It's a cool gadget going in search of a reason to exist.