Both are wonderful fragrances that smell quite different.
Pour Un Homme is predominantly a lavender and vanilla scent, but it's a very accessible lavender fragrance. However, if you don't like lavender, then stay away from it.
The Third Man (Le 3me Homme) is a floral fougère, sort of. It's sorta powdery but very unique.
I've tried Pour Un Homme a few times, but The Third Man I blind bought and loved it.