I imagine that most serious bikers that try a Nihola, or other trike, will hate their first ride. Trikes don't ride like bikes, they don't turn like bikes, they don't handle bumps like bikes.
It doesn't work to sit rigidly perched on top of a Nihola. It doesn't tilt into corners or point upwards when navigating a side slope. You tilt into the corners, you point upwards on side slopes. At moments when the trike is about to do something dramatic, you need to get a bit off the seat and relax, so that the trike can do what it is going to do, while your balance is not upset.
Consider how a person can balance on a trike like the Nihola. The contact points are the same as on a bike: hands, feet and seat. However the trike moves in various ways dictated by the road surface, none of which have anything to do with whether you are leaning one way or another. So you really ride on top of a Nihola, whereas you feel more one with a bike. At first, a lot of the balancing work being done by the hands. But the hands also steer the trike, and the steering feeds back into the rider's balance. After some time, I learned to balance on top of the Nihola with a lot less help from my hands, and this is an essential skill for anyone who is going to anything interesting on one.
Take for example a speedbump that extends almost the whole way across a road, leaving insufficient room to sneak a trike (or trailer) by cleanly. These are not terribly common in my experience (usually in Oslo the speed bumps give no special treatment to bikes, and usually in Copenhagen they leave a nice flat bike lane), but they are noteworthy. Both my wife and I got a bit of a surprise the first time we ran over the edge of one of these bumps with a Nihola, with just a week or two of experience. We were both sitting there on the Nihola, stiff like statues, and all the sudden the front tire encountered the bump. The frame of the Nihola happily and mercilessly followed. She says she just about crashed, I didn't quite have that experience, but it was a surprise anyway. The problem was that the trike pushed its rider around, and the rider pushed and pulled on the trike trying to stay balanced, including pulling and pushing on the handle bars, upsetting the direction of the trike. Conclusion: when navigating nasty stuff, get off the seat and relax.
A similar experience awaits when using a driveway to transit between a road and a sidewalk. One tire is going to hit the slope first, and if the trike is moving at a good clip, there will be some dramatic road-surface-following going on. Off the seat, relax, no problem.
When I'm riding around on a Nihola, I am comfortable enough to be a bit careless with balance, and sometimes I have to use my hands to save the day. Its important at those moments to be able to use the handlebar as a balance aid without turning it. Its just a skill to master like any other. There main motion here is pushing sideways (i.e. cleanly left or right) on the bar, to avoid steering. (Interestingly this motion is precisely what steers a trike like Christiania trike.)
I was not able to go very fast on a Nihola before I had developed a quiet upper body. The problem was that I kept making steering adjustments without intending it, very likely while maintaining balance using the handlebar. My first step was to concentrate on keeping my weight off my arms, but I graduated from that and now lean on the bar as much as I like.
Holding the handlebar in the center has a role to play with balance as well. I find that doing this frees my shoulders to move more and opens the path to more powerful pedaling, up to and including standing up on the pedals. But you can't do it before you get pretty comfortable with balance, because the hands have very little leverage to work with when they are right next to each other at the centerline of your body. I'm still working on my pedal-while-standing technique and am not very smooth yet.
So if there is a conclusion here, its that there is actually a lot of balance involved in riding a trike. People who think riding a trike is easier than a bike are being confused by the low speed stability of a trike. Try doing something interesting, and there is a lot of skill involved. And I'm not just talking about "you have to be good to not die if you pedal fast", I'm talking about skill that is required to do things that are safe.