Is this an appropriate replacement for our current bathroom extractor fan?
It's difficult to say without seeing the current installation. Rather than answering the question directly, I'll give you some tools to make the assessment yourself. 

There are a few basic considerations when seeking a replacement fan, aside from feature preferences...


Housing size
Housing mount type and location
Grille size (for coverage of the existing ceiling opening)
Duct size
Duct position


If any of those don't match, you'll need to decide whether the necessary changes are feasible and acceptable. That's mostly a matter of prerogative, so we can't say.