I suffer from poor distance vision and wear glasses. I started using a Clarifier Peep when shooting my Classic Scope with a 4X lenses. With out the Clarifier peep my target is a bit of a blur through the lense... with the Clarifier the target is in focus....... the down side is when shooting in a dark tunnel lane with a thick dark canopy at a dark target... the target almost disapears.
With different eyesights people choice of clarifier will differ .. what works for me or someone else might not work for you....... I went through many power lenses and different clarifiers to find the one and the right combination that works best for me.....

EXAMPLE
With a Classic Scope with a 3X lense I dont need a clarifier.
With a Toxonics 3X lense I DO need a clarifier.
Different power lenses made my differing manufacturers with differeing eyesight issues will cause differing results.
Also take in to account the distance the lense is from the eye on a slider sight, this will also cause differing results.
Its just one of those things you just have to play around with until you find the combination that works best for you.

I have used the GKF All Power Peep ... and the Specialty Peeps and liked both
( just make sure if you order the specialty peep get the one that is made for your degree or string angle on your bow... you can see this angle list at the Specialty Archery Website).