I have been using Dvorak almost exclusively for about 15 years now. It's not faster, that's a myth -- but it is much more easy on the fingers: depending on the nature of your prose, you'll save perhaps 30% finger movement. With Colemak, that number is less, but you gain a more comparable (to qwerty) shortcut-key layout.
Obviously, there are all sorts of adversities facing Dvorak typists: native hardware keyboard layouts, limits to the users ability to configure software keyboard layouts (for instance, you may be able to change it on your desktop -- but not on the lock screen!), and of course having to fall back to qwerty on other's devices.
Curiously, on a non-touch-typing device such as the touch screen of a tablet or mobile phone, I'm useless on Dvorak (perhaps exactly because Dvorak was designed for hand-alteration?), so there I'm by far more proficient with one hand on qwerty.
In the end, I think I will settle for showing them both layouts in use at their home, and let them decide which to use. However, @kqr makes a number of very good points, not least the RSI one.
There's also quite a lot of knowledge tucked away in this post: https://blog.hanschen.org/2010/01/30/dvorak-two-years-later-...