The following goes hand in hand -- obtaining a higher GH purity = a stronger synthetic hormone. With stronger GH = greater amounts of GH per IU. More GH per dose = better/greater results.
Thus, while you may be spending .50 - 1.00 less per IU on other gen's, it's certain their potency are not as great. In other words, to obtain the similar (GLO) results, you're gona spend more.
Further, lessor grades of GH *may* yeild unwanted results or at best, not offer as many desired benefits as pure GH does.
Something else to consider -- if you're purchasing from a China sponsor, note GLO's run 3 per IU. Compare this to 3.6 - 3.8 per IU for China pharm grade, such as authentic GenSci or GenHeal. Again, about .50 more compared to the GLO's, but quality (to many, that's important) easily surpases the GLO"s and so will the results per IU.
As said many times before - you get what you pay for.