Actually you are asking about only two head designs here. At one hand the Joris/Fatip (= Mühle R41/89 pré '09 razor head) and the present Mühle OC design which is similar to the Merkur open combs.
They are very different in nature. The Joris/Fatip/old Mühle is a razor with a huge blade gap and allows a lot of cutting angles, including a lot you don't want; so it is aggressive. It delivers a great shave but when you do it wrong it will bite. Very effective and efficient razor.
The Merkur/present Mühle head is very much milder as it has very limited cutting angles but they are chosen well. You can get a just as close shave from them but keeping the razor at the perfect cutting angle is a bit harder.
Same old story here; when you do it right both razors will deliver very close shaves. The more aggressive razor will be easier in getting a close shave at first but the milder one, once you master it, can do the same with no extra passes. When you don't do it right the aggressive razor will slice your face and the milder one will burn it because you use too much pressure or way too many passes.
Last edited by talibeard; 11-21-2010 at 02:28 AM.
I must to the barber's, monsieur, for methinks I am marvellous hairy about the face