I would encourage everyone who has the pro version who is upset about this move to go and post a poor rating on the Google Play store. I have already given it a poor rating and a comment on the Play store of my displeasure with this move. Not only will it lower the rating of the app, It may make others aware of it who may not be aware of it yet, and prevent others from looking into the app.
I to have moved onto Fairemail. Not only can you purchase it through the Play Store but if you do not use Google Play services you can also purchase it through his website.