(Germany only since the italians suck )
Now now, let’s not trash poor defenseless Italy. I love to play this little country, so I take it personally!
With Naval airplanes I have had both bad (mostly!) experiences with Germany and Italy and (some here and there) good ones.
But I still think (maybe biased) that it can make sense for Italy to do it (instead or as well as Germany) because they are one year ahead. And this compensate their lower experience (although I think 45 national XP could be better for Italian air units instead of 40XP but that is another question).
If I understand the mechanic correctly a newly arriving 1940 Italian Tactical (at 100% readiness) would have a Naval air rating of 1.2 while a German one of 1939 would be 1. For a Ground support version of the Naval air, the numbers would be respectively 1.6 to 1.5.
In 1942 (compared to Germany 1941) we can assume that Italy’s air XP is up to 45 (not such a bad assumption from my experience). So, for tactical type of planes, it would be 1.8 for Italy to 1.5 for Germany. For Ground support type it would be 2.25 to 2.
Also, I believe the opportunity cost is lower for Italy since they will have one less plane for mediocre ground support (Italy sucks even more at ground support) in exchange for an OK naval air. But for Germany, it will forfeit a very good tac probably for a mediocre, to OK, naval air.
But but but…, as I can also see the other side, this can change a lot if Germany catches up the tech on Italy or, if instead of building a naval air, they take one of their advanced tactical units at 60% XP let’s say and convert it into a 58% XP naval air. Now that is indeed clearly much more impressive...
Also, I did not calculate the defense value for each. Some year, Germany’s ones might be higher even if at lower tech.