Haven't seen it in play yet, but it doesn't look very good. If you already have dim lighting or darkness just use stealth and hide. The big benefit of invisibility is the ability to hide in situations you normally could not, but here you already can.
Now that doesn't make it useless, against creatures with darkvision for example dim light doesn't let you hide normally as they see it as normal lighting conditions.
So in play I see it playing out as the character is wanting to hide so he finds a dimly lit area or an area of darkness and then goes invisible, without this invocation he could still go into the dimly lit area and hide. Even with invisibility he still needs to take the hide action and make a stealth role if they want to remain undetected. Once the warlock moves or takes an action invisibility is gone.
Interestingly any action breaks the invisibility, so by a strict reading of the rules taking the hide action itself would end your invisibility, but that seems silly so I would allow an automatic hide action when you activate "one with shadows" so that one action turns you invisible and lets you make a stealth roll.