It may not be obvious at first, but you can always read user reviews for published apps on their app stores to see what people think of the studio's work. Just remember the negativity bias: people have more incentive to write a review when they dislike something than when they like it. One hundred bad reviews isn't so bad if the app has tens of thousands of active users.
Reading app reviews, keep in mind that some app developers engage in deceptive practice of buying fake app reviews that have nothing to do with an objective evaluation of apps. A good indicator of a fake reviews case is that if the bulk of the reviews have either 5 or 1 star, meaning the app in point has serious issues and its developer simply purchases fake review to improve its rating without fixing the problem.