It requires some time and a change in the way of use due to the rotating handle.
It's Felco, excellent quality obviously.

Maybe it fits better on my fingers, but I prefer the "sibling" felco 6, which I would give 5 stars. The rotating handle did not impress me, so 4 stars for that. Otherwise, the top quality materials are present here as well.

I bought the felco 12 for work in my vineyard, out of curiosity about what innovation it has to offer. As soon as I opened it, the quality was evident. The alloy they use is solid and lightweight, the pruner is well-oiled, and its blades fit perfectly. I chose this one among the other felco models because it is said to be the version of felco 7 for medium-sized hands. First impressions.

1 When I first held it, I started to wonder if I made a mistake and wasted 55 euros. The rotating handle turned very easily, and I wondered if the pruner would slip from my hand.

2 When I tried it on thick cardboard, the handle started to make sense, although it was still difficult for me to get used to it. When you squeeze the pruner, instead of putting pressure on the last joints of your fingers, like with a conventional pruner, the pressure starts from there but gradually transfers closer to the palm, making you feel the force you need to apply and the pain caused by the repeated pressure in the same spot. It may not be convenient, but the only thing I can say for sure is that it is not uncomfortable.

3 After several tests on roses, bushes, and cardboard, I believe that with a slight modification to the handle, the pruner becomes much more stable, and I started to feel that the only thing I can say for sure is that it is not worse than a conventional one. The more I use it, the more natural the handle feels, and the more noticeable the difference becomes when I go back to using a conventional one. I started to prefer the feeling of the felco 12.

My opinion:
Good materials
Good construction
Good logic
When fully opened, it fits perfectly in my medium-sized hand, so it also works for larger hands, but it might be difficult for smaller hands.
If not better, it is definitely different and difficult to grasp at first glance, but in no way worse. So, my fear of buying it and regretting spending my money disappeared.
It requires patience until you find a way to hold it, and definitely a period of adjustment.

It will be tested in long hours of work in the vineyard, and then I will provide an update. For now, 5 stars because it is worth it as a tool. Now I just need to see if it suits me.

Update: October 3, 2020.

Perfect. You can cut thick branches for hours without fatigue or pain. It is as durable as it gets. An upgrade from the conventional pruner in every way, with only one negative aspect.

If you do tasks that require constantly leaving and grabbing the pruner, it is better to go for a simpler pruner. It requires two hands to secure or release it, and a few seconds to properly hold it in your hand.

For tasks where the pruner never leaves your right hand, it is worth every penny.

Also, despite having average-sized hands, the pruner fits very easily in my hand, to the point where I am considering getting the larger size. My mother tried it as well, and besides loving it because she could easily cut branches despite having tendonitis, she has very small hands and it fit her very well.