Well, if you have a racetrack in your backyard with decent timing gear and a pit crew handy, I guess dynos aren't that useful.
For the rest of us with smaller backyards, trial and error on a dyno is a critical first step towards creating horsepower.
If you are SELLING crap, and you say "it makes more HP", unless you have a dyno, you are marketing, not engineering or testing.
My posts aren't a dig at any particular shop; there are several hundred shops today that say they engineer everything from scratch and extensively test all products to achieve the maximum gains, and their shiit is FAR better than everything else.
Instead, my comments are directed at the dillweeds who still post constantly that PPE doesn't actually make race parts. You know it's wrong, and you do it anyhow.