I just like the feel of Litmans, but don't want an adjustable bell and diaphragm. At least I can get it half-right...The diaphragms on the Littman III function the same as a bell with light pressure due to the design. Firm pressure makes the diaphragm function like a typical diaphragm.
There shouldn't be a reason to convert the pediatric side except for show. Now if that's what you want, then I do actually think that's a perfectly good reason. The kit will come with the bell adapter for replacement.