In our old house, we had a Manrose centrifugal fan that worked pretty well – even with around 2m of ducting in the loft.
When it failed, my father-in-law said he’d replace it. He stuck in a really cheap axial fan that just did nothing at all. Not the right tool for the job & within weeks we were getting mould forming on the ceiling.
I replaced it with another Manrose centrifugal one & back to decent performance – bit ugly though, as the box protrudes into the bathroom space.
It was this one:
https://www.electricaldirect.co.uk/product/manrose-4-inch-centrifugal-standard-fan-179726?vat=1&gclid=CPCHl-iHwdACFQsR0wodWV8KyQ
When we moved, the new house didn’t have any extractor. An electrican was doing a few jobs so I asked him to put in an extractor for the bathroom. Again, he put in a crappy axial fan, so not long after I replaced it with something more substantial. I bought an Aventa in-line axial fan, similar to the Manrose one that seems to be the go-to choice.
This one:
https://www.voltelectrical.co.uk/products/Ventilation/Extractor+Fans/Airflow+Aventa+100T+-+White/2689944809?gclid=CNjdpaOIwdACFccp0wod0PwNqQ
It works well. Admittedly, if I was doing it again, I’d have gone up to the 5″ version, rather than the 4″ just because, but it’s fine as it is.
In general – centrifugal fans are good at low(er) volumes with a higher pressure difference; So, they can’t push as much, but they can push harder. Good if you have lots of ducting.
Axial fans are good at high volumes with a low pressure difference; so they push a lot of air, but not very hard.
But, then if you can squirrel the actual pump unit away in the loft an inline axial fan is a good choice….