If I did a HW boost out of hours would it still run at eco, thats the only issue I see as it takes twice as long to heat up the tank. 

I don't know TBH but would guess so.

Does it use less kw consumption or does it balance itself out as the same?

Weird I know but am trying to keep my consumption numbers down whilst also having a comfortable home temp.

I think the fundamentals are this:

NR clamps performance at a particular level.  So most of the time it will make no difference.  When its cold enough that it does make a difference then yes it will reduce the energy consumption, but at the expense of the house cooling.  If NR is timed then the heat pump will have to work harder when the NR restrictions are removed, which may well cost more (its like a setback).  The easiest way to reduce energy consumption at the expense of the house cooling is to turn down the WC curve (and thus room temperature) a bit.

That said there may be some 'second order' effects, particularly with DHW.  Depending on the algorithms used which vary from manufacturer to manufacturer, NR might result in a less aggressive warm up cycle for DHW, which may well cost less at the expense of the space heating being off for longer and the reheat time being longer.  Some heat pumps have selectable DHW modes, which essentially moderate the aggression of the rehear, and NR may well achieve something similar to the 'eco' mode or whatever the manufacturer chooses to call it.

Best way to achieve lowest consumption (in most cases) is to operate with no external controls, at lowest WC consistent with keeping the house warm, and no buffer tank, LLH or PHE separating heat pump and emitters.  From that starting point tweaks may save a few percent, but rarely a lot unless the situation is one of the 'exceptions' (there always are exceptions!).  If you have a ToU tarrif lowest cost may be at a different operating point to this of course.

Does it use less kw consumption or does it balance itself out as the same?

Weird I know but am trying to keep my consumption numbers down whilst also having a comfortable home temp.