Reading through his care guides, the author seems to be a passionate hobbyist, but from skimming some articles I wouldn't use that particular blog for my care information. While I wouldn't go so far as to say this article is rubbish, the advice therein is completely impractical. As has been said, buying adult shrimp and acclimating them to new water is far from ideal, not to mention in over a decade of shrimp buying and perusing ads I can't recall ever seeing gendered shrimp offered for sale. I suppose you could grow a group out and cull extra males to such a ratio as they suggest, but offering a large enough space and lots of cover should keep females safe.
You will usually have a reasonably close ratio of males to females. I bought 10+2 Pintos about a year back and it's the only time I've had a noticeably skewed ratio. 11 males, only 1 female grew out of the batch. I'd think that's astronomically dumb bad luck, and that one female has been slowly but surely filling up the tank anyway, with a quite a few young females coming up now. I planted the tank heavily so she's been fine even with 11 eager suitors every time she's molted.
Nothing good happens fast in an ecosystem.