The revolvers are different frame sizes and require different speedloaders. The cylinder size is larger for the "N" Frame Model 28 then the cylinder in the K Frame M&P.
HKS makes speedloaders for both the K and N frame guns. You can find them at many gunshops or on-line.
The HKS Model 10 is for the K frame guns and the Model 27 is for the N frame guns.
Safariland also makes K frame loaders and they might also make N frame loaders.
I wrote reviews of both the HKS and Safariland loaders, if you aren't familiar with the differences between them.