As I stated above, we switched from MM to the t:slim, and are very happy with it. However, if your son likes the MM and is comfortable with it, I don't see any reason why he needs to switch unless he wants to. Medtronic will sell you a 530G without the transmitter and sensors. They just like to see if they can convince you to buy the whole package. Maybe get ahold of your local Tandem rep and see if they will get you a loaner pump so he can play with it. Our rep overnighted me a pump to play with over a weekend, along with an envelope to return it in. Their customer service is very good. If he's worried about learning something new, tell him it took my-then 9 year old about 3 seconds to learn to operate the t:slim. It really is super easy and intuitive. The one drawback to me is that the process to change a cartridge does take longer than on MM. But again, get ahold of one and let him play with it. And if still wants to go with MM again, don't make a fuss about it. MM does make good, solid pumps, and it really isn't going to affect his overall health one way or the other.