I did research on this stuff back in the 1990s. Made the films, did the vacuum chambers, had the world record for emission efficiency for a while. While it may have some niche applications, the basic problem is that it is *not* a low-voltage technology. Modern chips operate on 1.5 V or so; Diamond devices will be more like 5V. So ultra-low power? Nope. They say that the devices are more efficient because the electrons don't bump their way through the silicon crystal lattice. While that's true enough, it doesn't actually make a big difference. Why? Because the electrons very much will dump all their energy when they leave the vacuum and hit the anode.
Ultra-high speed? Again, while vacuum is nice in that it doesn't slow down the electrons, that turns out not to be a big effect. The most important factor in speed is the size of the device, and there is certainly no reason to believe that these vacuum tubes will be smaller than transistors, if built with the same lithography tools. I may be wrong, but I have good reasons to believe that they will be harder to make small.
High temperature? Radiation resistance? Maybe, but that turns out to be a complex question. These devices aren't just diamond and vacuum. They involve insulating layers, too, and those insulators may be affected my high temperatures or radiation. Essentially, a device is as robust as its weakest link, so until you can make the entire device out of truly robust materials, you won't gain too much.
So, it's nice work. I know how hard it is to do this stuff. And, it might be useful eventually. But it won't revolutionize technology any time soon. And, those guys ought to realize that, if they would let themselves. Research lives off publicity these days, because it is being forced to become more and more of a competition between groups. The trouble is, when competition enters and your salary depends on the claims you can make, truth tends to be (shall we say) over-inflated.
That darn free market ideology messes up science. I like it as much as anything for people who make spoons or telephones. But science isn't making spoons. If you get a bad spoon, you'll know it, but if you read an exaggerated research paper, how can you tell, other than by doing the research again? And, that's just not efficient: doing it wrong and then doing it again isn't nearly as good as doing it right the first time.
Oh well. Enough ranting.