The different between NPH (regular insulin) (maybe R too, not sure??) sold by walmart and Fast Acting insulins (Novolog, Humalog, Apidra) is massive.
Fast acting insulins start working at about in about 30 minutes and "peak" at like 2 hours, and may slowly have some effects for another 1-2 hours.
NPH on the other hand, starts working at ~2 hour mark and continues to work slowly until peaking at like 6 hours and slowly degrades away, that means its in your system for something like 9 hours - trying to meal plan around multiple doses of that is unsafe at best.
R is slightly better but still remains and slowly peaks closer to 4 hours.
These are obviously GREAT IF and only IF you dont have access to fast acting. I applaud Walmart for giving access to these, as they are way better than nothing.
source: Type 1 diabetic