I have some experience with Myrceugenias. I got interested in them for the same reasons as you and there are a lot of species out there.
My experience is that the Chilean species are relatively hard to find, but you can find them. I have grown Myrceugenia Chrysocarpa, M. Leptospermoides and M. Lanceolata. The last two have a very small and dry fruit with less than one millimeter of fruit flesh surrounding a couple of big seeds. The Chrysocarpa died on me at -8 Celsius, where my Feijoa's and Ugni's took a hard hit, but survived.
My conclusion was that in their own climate zone (8b, 9a) the Ugni and Luma species are far more promising than the Myrceugenia's I grew. Luma is quite variable but can taste really good. Sweet and creamy. And Ugni's are so aromatic, that it's hard not to fall in love with that little fruit.
I would be interested in seeds of M ovata v. nanophylla if you can actually find some. I have emailed that desertnorthwest website twice without any response, but that might be because I am in Europe.
The really interesting Myrceugenia's seem to be the Brazilian ones, at least for fruit purposes. But those I have never, or almost never seen for sale, and then they are adapted to the same climate zones as the Eugenia's, compared to which they have smaller and less interesting fruit.
That has been my experience