The Kerstar KV350, which I have, is a fantastically well put together twin motor upright vacuum cleaner and is similar to the Sebo BS36.
The Sebo has a more powerful motor (1300W) than the Kerstar (800W). I've found 800W to be perfectly adequate though, particularly at home where I don't like paying for more electric than I need to.
I'm not sure what Sebo mean by "hospital grade" filter as they don't qualify the term quantitively or with reference to standards. On first view though it looks to have better filtering than the Kerstar.