Using separate apps
Two apps means two places to look. Tasks and reflection drift apart, and a weekly review often means copying things from one app into the other.
Using FirmNotes
Tasks and writing share the same notes. The weekly and monthly reviews are built from those notes, so nothing has to be copied.
Where a separate task app fits better
FirmNotes is built for a personal day. If you need to share tasks with a team, a dedicated task app is the better choice.
Cost and accounts
FirmNotes is free to write, export and review, and needs no account. An account is optional, for sync.