Not sure what you mean by an NVQ being externally moderated.
When I did my NVQ Level 3 with my previous employer they just had to supply me with work that would meet the criteria, the criteria was set and moderated by West Anglia Training Association, though some people do their NVQs through college. It is a formal qualification, therefore has to be done via some kind of examining body. West Anglia Training would periodically send a training advisor to my place of work to see how I was getting on and make sure I was meeting the criteria set under the NVQ guidelines. Of course, the work is still done in the workplace, there are no classes to attend, but your work needs to be graded by an authorised training body.
Thats all I meant by externally moderated
But as Tris20 pointed out, it is very basic and probably beneath you. I found it was only good as an accompaniment to my other studies, if the NVQ was all I was doing (no ONC/HNC) then I can honestly say I wouldnt have learnt very much from it.
In short, an NVQ proves you can already do the job and know how to write about it, if you actually want to learn stuff then ONC/HNC teaches you theory etc.