Will that go away with practice? I guess the odd frame and small wheels make riding it unusual.
My guess is no. There is a chance it would be improved with different tire pressures (unlikely) or with a different person on it (very likely if front-rear weight distribution is affected).
I think there is definitely a learning curve. If you're on a good smooth surface, it's probably okay to use one hand briefly. But on an uneven surface, it's almost scary.
Fortunately, this isn't a bike you ride a lot. It's for the last mile problem with buses and trains and city areas. I might use it for orienteering when a park road is closed, or on one of our maps where you can access controls from a very long bike path.