Everyone is an expert...
To counter that, though, let me say that I'm not an expert on this kind of technology, but I did learn how to drive, and I can do some basic maths. This is an impressive feat, and here's why...
6 m is a very, very short distance to keep at 80km/h (=50mph). 80km/h is approximately 22 metres per second, so if you apply the well-known "2-second rule" for car spacing, it gives you a "safe" distance of 44 m to the car in front (66 m in the wet). So, this system manages to be safe at a seventh of what is considered to be the normal safe distance.
Sure certain [insert name of your least favourite German car brand] drivers manage to get closer to 6 m separation, but: a. it's not safe, because b. they're pricks who think that having a good car makes you a good driver.
The higher traffic density wouldn't be the only benefit - the other is that it would average out the traffic speeds. When roads operate at or beyond their design capacity, they start to exhibit chaotic effects - one ill-judged lane change can set up a "braking cascade" where the car immediately behind slows slightly, causing the car behind that to slow more, and so on, and then cars further behind change lanes to avoid the slower traffic, causing their own cascades. Within a couple of minutes, this can bring an entire multi-lane road can come to a complete stop, for no reason. (Which can bring the opposite carriageway to a stop as drivers slow down to see if there's an accident, and set off the whole damn thing again on their side).
Current solutions to this include the much-maligned variable speed limits on roads like London's M25 (drop the speed limit to suit the traffic density, give drivers more time to react properly, and minimise the chance of cascades), but there is also an idea to use systems like this one: traffic that can operate autonomously could be given its own segregated lane, with slower peak speed, but faster journey time overall.
For the record, I love driving, and I love cars, but motorways filled with commuter traffic aren't the place for heavy right feet - all you're doing is slowing yourself, slowing others, and getting angrier. The way I see it, the more people we can fit on the motorways, the less traffic there'll be on the more fun-to-drive roads..