I have a B+W 10 stop ND and it has a reddish cast. The Lee filter has a bluish cast. B+W also mentions the use of a IR filter to minimize the red coloration which probably should have been addressed to begin with by them (ahem!). Lee is cooler in color. You can use your camera's WB to account for some of it.
The B+W is a screw-in type, and the Lee is the slide-in one with the compendium bellows that clips on and off.
In use, I find the slip-in or using the filter's clip onto the Lee filter ring adapter much easier to use than the screw-in filters that take forever to mount and sometimes gets the lens spun out of focus a bit. Trying to focus through anything over 10 stops is a nightmare even for the camera so the filter has to go on and off. Taking the hood on and off and screwing a filter on is SLOW. The Lee set-up is much quicker in that I can clip the unit on and off much faster than screwing it on and off.
Metering may be off a bit too. I think mine is off maybe 2/3 stop more when using them. I have some charts made up in my bag when I use them.
SG
