Hi,
I completed my ATPL studying distance learning with NAC.
I used to study with OAT manuals, first because I had them for long time before enrolling at NAC, and then becasue NAC manuals are not really top-notch (but are being ammended).
Apart of that, really good instructors (available almost everyday, one is ex-Cabair, another ex-BGS)...but keep in mind that DL means that you have to do most of the stuff by yourself, an instructor can help but not really teach when he lives thousands miles from you.
My overall experience with NAC was great, I could plan my studies as I wanted to, a couple of weeks for the brush up in Naples (nice place indeed), helpful instructors and all first time pass with very high average mark.
Best luck.