I don't have one in my island unit. I had one many years ago and didn't think it was effective. This afternoon I've been out to quote on kitchen worktops and they had a wide chimney island extractor over their 5 ring gas hob. To me it stood out like a sore thumb. I certainly couldn't get used to it (especially as a person who doesn't have or like them). I felt as though I would bash my head on it. Based on that I'd opt for something in the ceiling so it's not blocking any view.

I had the same dilemma a few months back. I had new kitchen put in along with new extractor. it was at height of 70cm above gas hob. the extractor come out 50cm. I spent a few days trying to get used to it but in the end I was not happy and got the fitters back to raise it to 90cm. it looks a lot better and reduces the risk of me banging my head off the side of the extractor!. no problems extracting steam at that height. Glad I got it done as it would have annoyed me otherwise.

As a rule of thumb, you shouldn't make the extraction any worse than what was existing when refurbishing a kitchen, but part F building regs states any new kitchen should be provided with a mechanical extract fan, so is moving the kitchen to a new part of the house considered as being a new installation or a refurbishment. As I understand it (but check with local building control), providing a kitchen or bathroom in a room where there wasn't one before, building regs approval is likely to be required to ensure the room will have adequate ventilation, drainage and meets the requirements in respect of structural stability, electrical and fire safety. You would need either a 30 litre/second extractor if its over the hob or 60 litre/second if its placed elewhere ie on an external wall to meet part F. But you may also have to consider/meet some of the other parts of the regs. as well. Be interesting to know if you do ask building control what their answer is (get it in writing from them so they can't change their mind).

We have a powerful bathroom style centrifugal extractor with grilles above the oven stack and the hob (slightly off centre due to lighting/beam constraints). Reasoning was that I didn't want to box myself in or obstruct view of garden with a hood extractor and we couldn't get a ceiling extractor in for reasons above - plus they are ££. A downdraft was out of budget. Also, I wanted the least dB possible. It works really well. Ceiling is painted matt white and there is no grease on it after 2 years and I do do lot of hob cooking. The grilles are super easy to wipe down - I do it every couple of months, takes 5 mins.