Having Googled this with all the obvious words, I'm amazed to find that there doesn't seem a dedicated post or article about it.
I own the Lee filter system and 3 ND grads, all of which I originally bought for my 35mm rig. Now that I own a Hasselblad, I'm buying the appropriate lens adapters so that I can use it with that too. However, I've been looking at the dreamy softening filters that both Lee and Hasselblad do or have manufactured.
At ffordes.co.uk, as an immediate example, there are several second hand Hasselblad Softars 1, 2 and 3 (http://www.ffordes.com/category/Medi...Series/Filters) for around £30, give or take or there's some brand new ones for about £150. An equivalent 'Lee Glass Soft Focus No2 Filter' also comes in at around £150 brand new (http://www.dalephotographic.co.uk/ma...20No2%20Filter).
So - which are better, optically? Lee or the Carl Zeiss Hasselblad ones? I ask because I'd prefer to keep collecting to my Lee set so that I can use it with both my Blad and my F5 but, if the Lee filters are no where near as good as the Carl Zeiss Hasselblad ones, then I'd rather build two seperate sets - one for my Nikon and one for my Blad.