Of those, I know that K&M offers a carbide reaming/turning mandrel, and has an expander die system. I don't remember if K&M has different angle cutters or not. But with a K&M, it's easy to view the cutting, and it's easy to clean(being an open design). Some folks don't like that K&Ms are so small.
They are all easy to adjust.
The whole eccentric mandrel adjusting is insignificant as a benefit really.
I don't like either. Sinclair has the best 'system' IMO.
Neck turning is not a no-brainer-throw it on a bench-and turn em all,, like trimming.
Often, it takes a strategy and the more options in your SYSTEM, the better.
I can't compare as I only have K&M's, but I like them enough to have bought 1 in the two calibers that I neck turn for.
They are also priced such that you can afford to but one and set it up in those chamberings and leave as is. A much better priced deal than the Sinclair IMHO. Others may disagree.
K&M now offers a sort of jig to aid in setup, but it is certainly not needed, but I got one of them too as it does help. The K&M is easily adjustable. The cutters are sharp and I think you can get a different angle for the AI cases.
And yes, I do generally like Sinclair's products and I have several....
Either way, get the matching expander mandrel of the same manufacturer.
I cut with an electric screwdriver, feeding the case slowly and my cuts are extremely smooth without any ridges.