I've just done it, and I love it! When I trained in spmu originally about 15 years ago it was soft tap that was around and the machine trainers kind of looked down on manual as being old fashioned. You can obviously do hair strokes with machine method but my experience with this is that I feel calmer doing this....does that make sense? I originally was attending a brow refresher day with my machine, my model had a few different old pigments and methods in her brows and were beginning to look very blocked and solid...the trainer asked if I would like to try the manual pen to go through with other colours to make them more 3d looking....OMG what a difference!
It seems to be less traumatic on the skin, I have no, or very little bleeding, better colour retention and the clients have no more redness than if they had been waxed and it takes half the time with less than half the treatment cost. You can also buy fully disposable pens (blades in a holder) so should not need an autoclave etc....
I disagree with the 3 years though, 1 year to 18 months.
I trained with The Brow Studio Group, Louise is lovely. It's called Epibrows.