I have the EGW-U dies in 9mm and 40 S&W and I never use them. So based on my experience, save your money.

First of all, many of the pictures you see of "Glocked" brass, is really brass that is fired out of battery. It is true that Glocks have generous chambers, but this results in a bulge more toward the mouth of the case, not the guppy belly near the head.

For 40 S&W I use a Lee carbide die for sizing. Since the taper at the entrance is less than other dies I have (Dillon, RCBS, and others) it sizes the brass better. On a very small percentage (less than 1%) of the range brass I pick up, it will not fit in a Lyman case gage. That is the way I check. Yea, it still would probably chamber and fire in a Glock barrel. But I use Lone Wolf barrels since they are tighter for future loading and firing lead isn't an issue.

For the 1% that don't pass the Lyman check, I have tried the undersize die, but I found at least half didn't pass my Lyman test. And it left an ugly step at near the head of the brass. And I wasn't too excited to work the brass that much.

So as OKFC005 mentioned, running them through a Lee Carbide FCD solves the issue. I run brass not fired in my pistols through this die the first time I size them. Never have to after that. 100% reliability after running them through the FCD.

Just to let you see various pistols support: