I am using copay on my windows wallet and it works flawlessly but the only worry I have is I don't know any way of importing the backup to any other wallet, which is why I am afraid of sending any big amount of coins to it because if for some reason it doesn't work tomorrow I have no way of getting hold of my funds.
Agree, we know that the backup process needs to be improved. But, regarding to import to another wallet different of Copay if for same reason bitcore-wallet-service stop working, let me say that you (or your company) could create their own service to use with Copay. So, with your backup and an alternative bitcore-wallet-service, you will never lost your funds if something going wrong.
Copay uses
Bitcore Wallet Service that it is also open-source
https://github.com/bitpay/bitcore-wallet-service. After create the service, change the BWS url from preferences and "recreate" the wallet with all your funds. That's simple.
It is also missing some features as importing a paper wallet, sending to multiple addresses etc.
We have these features in our plans.
Thanks!