Just done mine a few days ago now, had a spare hour, very easy to do once the car is raised, my sleeves were so old the bolts were gone, and the crappy A clamps were so corroded I wangled them off with a screwdriver. If I had a few quid more I'd replace the U pipes for something shiny but the old ones are perfectly usable for now, so a good clean and some paste has made a good seal.
It has made a big different in how the car idles now that there's no gases escaping, very smooth, and it now sounds like it should with a throatier burble, so sounds awesome just pootling around the lanes. More importantly it now passed it's mot.
Thanks Boxob for the how-to, very helpful.