It should increase APS by 25% on gear so if APS is 2, then it would be 2×1.25= 2.5 APS. The DMG increase by 25% at (5) should be as big as like using Defiant (5), Pathfinder, Relentless, anything that increases DMG by % . It's not MH% that's for sure.
It's like using 25% attack speed but on a set and increasing the APS directly whilst increasing your DMG output by 25%. This applies to skills below 1 second which is a big key here.
Hunger increase attack speed by 37.5% at (5) or ×1.375 to APS so if i have 2 APS, this increases to 2.75 APS.
For skills, APS means how many attacks you could do in 1 second. 2 APS means 2 attacks per second . Well that's what i believe anyways from testing but not sure. It's a complicated issue though as some skill from some class work differently .
You will need below 1 CD or 0 CD.
Also this guide should really help you get an idea on APS.