You keep referring to "other" pre-workout supplements but you don't mention any specific one, so your not helping your cause by trying to differentiate between those and n2amp. Some might contain dmaa but there might be other compounds in the supplement that isn't in n2amp or the dose could be different, there are a ton of different situations that can come from these scenarios. So instead of going round and round, why don't you list a few pre-workouts you are thinking about so we can make a proper comparison and tell you the actual differences.
On another note, non of us here have any reason/requirement to push/promote these products. We chose to do so because they work. I am not a rep for needtobuildmuscle just like most other people on this board.