I've had the Ambassador on my last two boats - both equiped with Volvo saildrives. Invaluable piece of kit. The anode needs a bit of machining to make space for the cutter. This involves making a slot across the top of the anode so that the head of the cutter fits snuggly. Ambassador can supply them already machined. Alternatively you could take a saw and file to it - personally I've gone with the Ambassador arrangement. Its worth buying a couple at once so you've got the next year's replacement handy.
I have used both the Hayles and Ambassador cutters on different boats. The cutting action on the Ambassador is superior, being serrated, and the bearings last infinitely longer than on the Hayles model - a real cost consideration! The Hayles cutter can also run more easily out of alignment as bearing wear progresses, causing uneven blade wear that needs machining to correct (personal experience)
For the S Leg (which I now have) you really don't have much option than the Ambassador, you lucky bloke! The anode is machined by Ambassador to just slide on. You can buy regular S leg anodes and drill out the top section to secure against the S leg, but having tried it, it's not worth the trouble.
This is not cheap gear but then the stresses involved require a quality build. But the saving is well worth it every time - the cost of a diver or towing launch/ tug can seriously dent the galley kitty!