The blade in a slant cuts smoother all the way along, well I think it does anyway.
I have (I think) a Merkur 37C, which is the one with the shorter handle. It is currently my every day razor and has just pushed the Weber ARC into my travel bag.
As far as I know the heads on the Merkur razors are the same, it's just the handle length that is different.
The way I think it works is that when you shave with it rather than the blade cutting at a 90 degree angle to the blade of the razor, it is slightly off, so it slices slightly sideways. This makes sense as to why it is easier, think about when using a knife to cut something, you rarely just push straight down, you pull or push the knife as well so the blade runs along the surface of what it is cutting. This is the same principal as what makes the slant work so well.
A slant is certainly a fantastic razor, especially with a nice sharp blade.