Really don't even need a device. I practice balancing on one leg with my eyes closed while brushing my teeth every morning (I've progressively made it harder over time). I mostly do this to keep up my balance skills for mountain biking and it's helped quite a bit, especially during winter when I ride less.
You mentioned progressively making it harder, I’ve seen the following strategies to make balancing more difficult. Combining them all can be challenging:
1. Arms crossed on your chest
2. Eyes closed
3. Swinging your head left and right, like an exaggerated “no”
on the opposite end of simple-or-cheap, e-foiling Does train your balance. esp. in windy "cabbage-salad" waves with medusas and rubbish floating around :/
Does it though? Balancing doesn't seem like an active cognitive process, like I don't have to think about not falling over to stay upright on a bicycle. All the little shifts of body weight needed to not tip over seem to be done automatically.
The most likely outcome, provided it doesn't lose too much speed, is to hit an obstacle. This happens all the time with motorcycles which are just heavy bicycles. The angle of the forks causes the bicycle to self-balance.
Not on a balancing ball. It's far far harder than staying upright on a bicycle. You have to stay focused and control several muscle groups. Not falling even for a minute is a very challenging task. Being able to balance for 10 minutes is basically elite level.
