Tough not my area as well, I am pretty sure this one is not good.
The signature is slightly shaky indicating that it was written rather slowly and carefully (see e.g. the last line of the "N", the "A" or the "g").
Furthermore, I guess, Armstrong wrote the "l" differently (higher and less curved) and also the transition from "t" to "g" is abnormally kinked in my opinion.
+1 for this being a fake most likely, Doesn't look quite like Neil's signature compared to genuine ones i've seen. is this being sold on eBay? whats the price point? sometimes you can easily tell its a fake if the asking/selling price is too good to be true.