Getting ready to upgrade. Currently have the MM 522 (holds 180 units). Thinking about going to the 723 (holds 300 units --can also take the smaller cartriges.) Looks like a little over a half inch difference. From the Web site. "How small is the Paradigm Revel Insulin Pump? The Paradigm Revel Insulin Pump is about the size of a cell phone. The Paradigm Revel 523 Insulin Pump measures just 2 x 3.0 x 0.8 inches and the 723 model is about one half-inch longer in length (0.6 inch longer) -- exact dimensions are 2.0 x 3.6 x 0.8 inches." WWYD for an 11 year old? Current TTD is 22 -30 units, but this will change with puberty. But i like how small the 522 is.