I have never used ACT magazines in an M&P. Generally, I believe they have a good reputation and have had good experiences with their P226 magazines.
If needing range mags, you could give the ACT a try, and they are probably gong to be good, and cost about half the cost of the OEM, but for other purposes I would use the OEM at least until fully vetting the ACT.
ACT mags for the M&P are available and in stock from several sources.