I do carry an extra magazine for a deep-carry handgun when wearing summer cloths, but not the product that the article (and SA?) appears to be endorsing.
The product in the article looks to be bulkier than the NeoMag I use so I wouldn't consider the articles' product.
I think the article has merits but should have discussed (compared & contrasted) the other types very low-profile pocket magazine holders like the Neomag, Snagmag, etc.
My .02