I have had a Suter clutch for quite a few years now. Great bit of kit - I wouldn't go back to not having a slipper on a big Vtwin. Good on road but even more needed on track. The Suter works differently from a conventional clutch in that it does not use the six springs to keep plates together. It used the standard clutch plates but has a large round flat spring which are available in different strengths so you can fine tune the amount of slip you get. But Colonel Link and I had issues with clutch slip last year and had to uprate to a heavier spring which cured the problem. We think that the SD engine with Motobox and full exhaust system just makes a bit too much power for the recommended spring. There is a big thread on here about it all if you search.
Here it is....
viewtopic.php?f=18&t=19360&p=231345&hilit=+suter#p231345They are good clutches and you can deal with Suter themselves for parts and advice but there is a bit of an issue that they say that you have to talk to KTM and KTM say you need to talk to Suter. I have a 'Suter" clutch that I bought from ebay but it is not a KTM hard parts clutch. It is EXACTLY the same unit though.
Good luck in your choice, I'm sure that both Suter and STM are both good choices.