Been eating bananas the correct way for my whole life. Was taught as a kid and my kids have been taught.
As for if they are good for you, they make a good snack to eat without other foods. The carbs are fine if you are going to be active and these calories can be burned quickly before being stored for future energy (fat). I like to have one before playing sports and drink water vs Gatorade or other "sports" drinks.
Definitely good for an energy boost!
I used to laugh because an overweight lady-friend of mine was always struggling with diets. She'd eat tons of bananas because supposedly they didn't cost her any "Weight Watcher points" or something.
Everyone and their diets. It's all about eating what you like, but eating within reason. You can't starve yourself and you can't stop yourself from eating things you enjoy or one day you will break...or at least most will. Learn to eat in moderation and when to eat different foods. Some people have a sweat tooth and that is fine if you can make sure to eat those treats during the day before activities. No different then the banana, you need to burn off all those sugars asap.