Not all lancets and lancing devices are created equal. Some are smaller, which means they hurt less for small children but might not provide an adequate drop for older kids. Some lancing devices are easier to use than others. Lancets are not much good without a lancing device to hold the lancet. Basically, how much does it hurt.
Comfort is more than simply having a small diameter shaft.
The quality of the grinding of the lancet makes a big difference, as does the quality and adjustability of the lancing device. Ease of Use . We all want our kids to do their own testing. Some products are easier for little hands to use than others. This mostly applies to the lancing devices, but some lancets are more troublesome than others.