It looks like:
http://www.koni.com/FSD/frames/product/program.php
it might only be front struts / dampers / shock absorbers (which ever you want to call them) for a Mazda 6, needs to be checked with Koni.
£315 including VAT (sales tax) is the best price I know of for 4, fitting costs are extra.
It is not cheap, but then you pay this much for 4 decent tyres.
It all depends on your budget and how far you want to go to optimise the ride and handling of your car.
In my opinion the Mazda 6 is one of the very best handling 4 door family cars you can get and as you are a 2.3 Sport owner I thought you might be intersted in going just that bit further to push your cars ride and handling to the best it can be without more serious surgery on the suspension system.
The reviews for the Koni FSD are so glowing you might just think it the best £315 (or less if you only need 2) you've spent on a car. They are standard fit on the Lamborgini Gallardo.

 

It went in for a 25,000 mile service yesterday and they confirmed that the rear dampers were 'weeping' (I didn't think I was that unkind to them!). Anyway, they've ordered the parts and will fit them under warranteeso we'll see how it feels after that.

I'll review the Koni shock absorbers option later. 4 new tyres needed soon (3mm all around) so that will have to come before luxury shock absorbers.

I have to say that after the 25,000 mile service the car feels 1000% better anyway even though they've done nothing yet to the suspension/shocks/steering/tyres etc. My 6 always lets me know when it wants a service.

 

Had a feeling there would be a "problem" causing the bounce since this is not normal for a 6.
Only worth doing the Koni FSD's if you feel you want better body control without compromising ride after the new dampers are fitted.

 

Well...

It took three weeks for the part to be available for my new shock absorbers (rather surprising for just a set of rear shock absorbers/dampers). But today I had new shocks fitted and I must say that it feels a good deal better.

However... there was some confusion over the courtesy car they had arranged (i.e. they denied all knowledge of the booking). So they gave me what they had available - a Mazda Truck (BT-50 Double-cab, 2.5 dielsel turbo). It was enormous and silly (as atemporary replacement for a Mazda 6) but I enjoyed it for a day (any longer would have been a bit annoying). So any improvement to my 6 was difficult to judge after driving a tractor around for a day. Perhaps they did it on purpose!

Anyway - I love my 6. And all is well.

 

great to hear you got it resolved.. While the konis are great shocks they require more modification to the front struts than i would like.. You can get Bilsteins that pretty much drop right in.