On the Tonight Show last night, they showed a clip of an 88 year old woman using it. I must admit, it definitely got me interested. But before I buy one, I'd like to get an idea of what kind of apps they have for it and how many apps are currently available. I've seen a huge variation in prices, ranging from $15 to $120. What's the difference? Is a $120 model really that much better than a $15 model? Also, just want to make sure it works with an iPhone 6 Plus.