I recently bought a Nilfist Attix Alto 30-21 PC (I think)
It was around 230 from D&M tools, (beware - the floor cleaning kit is another 60 quid)
I love it to bits. It's quiet, works well with the hand-held 9" Makita circular saw (though I had to cooble up and adaptor), routers, and again with a bit of cobbling a biscuit jointer. You can plug the tool into it so it starts when you start the tool (and over-runs for a few seconds when you stop).
You don't need bags, and you clean the filter by blocking the nozzle and pressing a button a few times. It's fairly heavy - I have to carry it upstairs when Mrs Tim Nott wants to use it, so I imagine the 50 series is heavier.
The tool hose is generously long - (hint use cable ties to keep it and the tool's power cable togehter)
My one gripe is that the floor kit dosn't have the tube diameter to cope with big shavings (eg hand plane) or splinters. It seems you can get a 50mm hose, but according to D&M it costs the earth