I've used it for about six months now. It was/is missing a few bells and whistles (like a good quality scripting API to enable something like Vagrant, which I talked with their team about doing), but overall it's extremely robust and the lack of kexts needed makes it an immediate winner despite the few gotchas.
There's actually a Vagrant plugin to use Veertu as a backend. You can find the underlying CLI that the plugin uses in /Applications/Veertu Desktop.app/Contents/SharedSupport/cli if you want to script it yourself.
The difference between VB and Veertu is that the latter is much less invasive (so less potential for screwups and problems with other invasive solutions like VMWare Fusion) and it's potentially much faster because it leverages the Apple subsystem. VB has a chequered record on OSX.
I like Veertu, but I'm a bit sad about the increasing level of fragmentation in the virtualization space. Where before you had a couple of products, you now have dozens of mostly incompatible ones. I have team-mates pushing for Hyper-V since they're all on Windows, I don't like VirtualBox and I find it more and more difficult to justify spending money on VmWare licenses, considering they are not significantly improving desktop products. I wish new players like Veertu offered better interoperability, i.e. export features as well as import - although I understand why that might not look as being in their best interest.