I have a Glock 41 Tier 1 by Salient and a Glock 21 by Black Box. The frame work, ie, stippling, frame reduction and under cuts are of equal quality. The slide work is also of equal quality, at the time they did my G21 Black Box was only doing front serrations, tri top and RMR milling.... they since have add more slide lighting cuts.
So the only real difference is having a hand fitted trigger. With so many quality companies offering high end drop in triggers, the difference is only minimal.
Yes both are expensive compared to stock...... but isn't everything custom. Whether it's cars, boats, bikes, or you wife's boob job. Some people want something custom and some people don't......90% of the time is the difference between people who have disposal income and those who do not.........
Now when I bought my Salient the dollar was par......now it's 40% higher.