Halfbike is an amazing toy for young and grownups... I got it 3 years ago to learn at the same time I was teaching my kid to ride regular bike. It was very fun. Now I also use it to exercise, with rides of 1-2 hours (20-35 Kms) per week, the effort required is good without the need to leave the city in search of slopes for regular or mountain bikes.
Don't think it is just start riding, it is a new experience and the skill needs to be developed, this to me is part of the fun. Be sure you do it using the appropriate protection gear.