gStrings is a chromatic tuner with a VU type meter, Melodica-Me. I’m with you on the type of meter. I’ll get one of the Korgs and see how it compares. I don’t think the cost of an app means much. The hardware I’m using is a $500 tablet computer, and we know that a lot of the best operating systems, software programs, and applications are free. Linux operating systems, for example. Fortunately, a lot of developers are not in it for the money.
I take your opinion about 440 vs. 443 very seriously given your background. For my purposes, it doesn’t matter much, since I’ll never be pulling out my P-32D melodion or a Bosendorfer on a gig. But, unless my readings on a bunch of melodicas are way off, almost all of them come factory tuned closer to A=443 than to A=440. I have no vintage melodicas so don’t know whether the same applies to them. But if the standard for performance is 440, then there’s a lot of tuning to be done, especially if the emphasis is on establishing the melodica as a respectable instrument. Everyone who’s using melodicas on gigs needs to get their melodicas down there, either by learning to tune or by contracting the job out to a professional.
Complete tuning to A=440 (or whatever) is a challenging project. But bringing a handful of your flattest and sharpest keys roughly into tune with the rest of the keyboard isn’t, and that’s the sense in which an ordinary schmo like me can tune his own melodica.