Personally, I wouldn't waste time and money grafting unknown seedlings onto clonal rootstocks. Even if I was interested in fruit quality, just plant the seedlings and wait. You could easily raise dozens or hundreds or thousands of seedlings. You can't get hung up on whether any given one will be a good or great apple. Every seed in every Honeycrisp could have been the next great apple and only a tiny fraction of those seeds have ever had the chance to germinate. Better and cheaper to be patient and ruthless. If a seedling dies, so what. It wasn't meant to be. If it grows too slowly, pull it up and toss it. If it shows disease problems, pull it up and toss.