I am joe and I have been using minimed pumps since 2005.
it is very likely that the physical pump - “the brick with the clip”, is fine.
most adverse reactions with pumps all center around the delivery system and all pumps have the same basic weaknesses. This delivery system is some combination of tubing (yes, even in a omnipod) and a local catheter that is supposed to deliver insulin at the “subcutaneous” level.
given your grandson needs 5:1 saline, he is very sensitive to insulin, which could always be an issue with lows. this typically changes as your grandson gets older.
the catheter he is using is very important, they can be straight, angled, teflon, or steel. Based on what I have heard, many people have problems with the straight-teflon “infusion” sets. most notably in children. If you work with minimed - you will find out they offer different infusion sets and if he is not on a “sure T”, in my opinion, he should try it.
given the sensitivity, he would still need diluted insulin with any injection strategy, such as a syringe or pen. in my opinion and experience, if you can figure out the delivery problem, the pump tends to be the most versatile and accurate.
with 30 plus years of experience, I get highs and lows. it’s not a failure of my pump, it’s just that perfect blood sugar is like a tiny target at 200 yards. in my pump’s “90 day history” my highest high was 290 and my lowest low was 39. If you think about the variability of activity, food, the inaccuracy of a home blood sugar meter, and the absorption of insulin, it’s a miracle if my bg is between 70 and 100 mg/dl.
good luck and please let us know how you are doing