It's up to you! A deadbolt smart lock may be a good choice if your existing lock is a deadbolt. If, on the other hand, your existing lock is a mortise, it may make sense to install a mortise smart lock like the Aqara A100 or the Aqara D100 in its place.
Some applications where the Aqara U100 Deadbolt-style lock may perform better:
Your existing lock is a deadbolt lock
You have a long, vertical handlebar that doesn't leave much space for the bigger A100 or D100
You want to retain your existing handle lock
Interior doors
You have an existing lockset that may leave holes when installing the A100 or D100 - in this case it may make sense to install the U100 above your existing lockset