If you look at the relevant meta-analyses, the effect size estimates are quite modest, so much that most of nicotine's cognitive benefits won't be detectable by introspection. Given the lack of readily observable benefits and given the foul taste of the gum/lozenges, it can be challenging to maintain the habit. All this is in accord with my experience. I would expect that e-cigarettes are superior in this respect.
I'm closer to personally experimenting with nicotine, so I'd like to gloss over these meta-analyses. I can access academic, and medical, journals myself, but I don't know which ones to search in. In which journal can I find this citation? (please and thanks).
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.