Absolutely. Inputting transactions manually is a great way to instantly update your Safe-to-Spend and keep you present when you're spending money.
Manually added transactions will be automatically matched to transactions that sync from your bank account for the same amount. If a transaction is matched it will have a checkmark next to it on the Dashboard and you won't be prompted to review the matched transaction from the bank.
If the transaction you entered doesn't quite match the amount from your bank it won't be automatically matched. Instead, you will have the option to match the transaction yourself on the confirmation screen as shown in this sushi example.