HiddenVM seems hacky and unstable, and a similar effect could be achieved with a few simple commands. Like encrypt some partition via LUKS, save the header to a file, dd the header with data from /dev/urandom, have only random data on disk, dd the header from the file to the disk, have your working partitions back. You don't need a windows app like veracrypt for that. As a matter of fact, I find it suspicious, that they're using windows apps. Besides, I don't think, that tails is meant to run as a host for VMs. It's already running from memory, so the demands on the hardware will be very high, tails uses a customized and hardened kernel, which was built without having VMs in mind, it requires installation of unhardened packages from non-tails repositories, requires you to run custom code, and all of this might lead to bugs or backdoors destroying whatever additional security tails provides. Hardened operating systems aren't made to be as versatile as unhardened ones. The idea behind hardening is, that you lock down every kind of functionality until you're only able to perform one simple task, and nothing else. That's hardening. All those fancy ideas with OSes running on VMs which were set up with some windows crypto tool and so on sounds like it's trying to get around the hardening, and therefore decrease security. Hardened OSes only allow you to perform a few tasks for a reason.