You actually don't need an app to add Suica to your iPhone, it's added directly from your Apple Wallet (so maybe that's why the "app" has poor reviews, not sure what the app is for). This is generally the easiest thing if everyone has their own iPhone since no fumbling with cards and loads easily with Apple Pay to avoid payment issues. I think it even works if your phone is out of battery. You can load money into it using Apple Pay, I think it used to be limited to Amex/Mastercard but may now be allowing Visa depending on your iOS version. I think you can also load money at the stations.
All you have to do is open your Apple Wallet, hit the plus sign to add a Transit Card, and type in Suica. Sooooo easy! In fact, I just set mine up now in about 60 seconds. Selected a card from my Apple Pay and added 1000JPY. No payment issues at all! I think the limit is around 20,000JPY ($128 USD). Many places take Suica for payment like convenience stores!
Edit: You can also add your existing physical Suica card to your apple wallet from what I understand, but then the physical card will no longer work. But it would be handy for someone that already had a card with a balance and preferred using the wallet version.