Pay to win
Topps has been changing the rules for ongoing series, always making the card sets less interesting and putting The more rare cards behind paywalls. So the only way to get some cards is paying, and they are never too explicit about the changes. Beyond that, the trading feature is terrible, the app is really sluggish and it drains a lot of battery. Collecting cards is fun, but its really sad to see the greed taking over and the app itself not evolving.