While I am running without the phone so far (hence not using the app, but maybe I should), let me add few comments.

* Mapbox GL can display raster maps as well. The tiles will be slightly blurry (issue https://github.com/mapbox/mapbox-gl-native/issues/10076), but its simple and possible (see example style in the same issue). And you will be able to draw on top of them using its API.

* Using classical raster tile implementation implies that you have to deal with the downloads. Mapbox GL takes care of it leading to simpler code for you. Same goes for keeping cached tiles or vector data - Mapbox GL has it all implemented.

* OSM Scout Server works best if you request larger than standard raster tiles (1024x1024 is used by Poor Maps). It boils down to efficiency in rendering bigger tiles that take care of reducing label cutting on the edge. So far, in addition to Mapbox GL, only Poor Maps has been able to request bigger tiles. Hence the performance of Poor Maps vs modRana, for example, when rendering tiles from OSM Scout Server.

* Mapbox GL is way faster.

* I think you'll be fine with 50000 downloads. Don't forget, vector tiles are cached. When people run they tend to take the same route or at least the same region. Hence the cache should be resolving lots of requests. Right now, while admittedly with the bug in online download for few days, during 6 days we had 3000 requests by Poor Maps GL users. @otsaloma, though, knows better with his stats of Poor Maps and tile downloads.

* As for disadvantages, the hardware limitation is summarized at https://github.com/mapbox/mapbox-gl-native/issues/10029 . In short, J1 and Photon Q failed, everything else was fine. Although I have one user reporting issues with Jolla C and OSM Scout Server vector tiles.

* The other disadvantage of Mapbox GL: you will not be able to get to Jolla Store. Assume: ever. Be surprised if Jolla allows this API.

In my eyes, its just so much easier to program with Mapbox GL. Don't underestimate the time you have to spend on many aspects of map drawing, updating, caching.

PS: I do wonder whether I am biased...