I wouldn't use them. There are multiple supports of people losing their funds and supposedly getting scammed. And since you don't control your private keys, I wouldn't be surprised if that was true. Why even risk your coins by giving them to someone who has full access to your coins and can take them whenever they want?
If you get your coins back, do yourself a favor and create a safe wallet.
TryNinja, we research all user complaints, and most of the issues that are coming up turn out to be user-related: people make transactions to addresses of a wrong network or without a proper payment ID; there can be delays with transactions due to the current network state (especially with Bitcoin); sometimes there are troubles with exchange services our partner provides. Any live service on a highly volatile market, such as the crypto one, can expect to encounter issues eventually. We're doing our best to assist our users with resolving them ASAP.
Regarding being a custodial wallet, we're not the only one on the market. This business model has its pros and cons, and every user decides whether our app fits their needs.