Well aware. Listening to Aitana and Joy cantando en español, for instance; the former uses the th, while the latter does not.
Same thing happens with English speakers in the US, where I can’t understand some of the English accents and they can’t understand mine (though the unexpected dinner order was delicious), and I always sound “from away” to others. Was listening to what I thought was a singer from Boston a while back, and she was from northern England. Whoops.
I’ve come to accept that my own accent will always be atrocious.
Back to your concern… If the app is using the Apple voice synthesis pronunciations as it appears, well, go for it. I’d still expect issues absent time spent listening to and talking with some of the locals. The Apple voice synthesizer is quite good, but will definitely miss regional accents. Most of the apps I’ve worked with embed recordings of native speakers, which I prefer to the synthesizers.