A few of years ago, I watched a fascinating illustrated talk by Guy Edwardes, who shared a few of his images where he had used a 10 stopper, so I fancied a go at that.
Now I have been a Lee Filter system user for a good few years now, but at the time, the Lee option on the 10 stopper wasn't available. The only options were Singh-Ray and B & W, although I am sure there might have been another one.
Both of these were only available as a screw in option. Now I thought it was a bit of a faff, because as Dave says you really cannot see through it once it is on the lens, so you have to do your composition without it on. Now with a drop in filter this is obviously quite easy, and relatively quick.
With a screw in, it is more problematical, particularly if you also want to add a drop in system on top as well.
Now where as Dave was seeing a strong blue cast, with the B & W, it wasn't blue but more brownish as you can see below.
Nothing special really. You can get quite nice cloud effects provided there is some movement. Usually works better if the clouds are coming directly towards you. Colour cast not too bad here. This was taken at sunset on the 1Dmk3 a couple of years back at Bamburgh Castle in Northumberland. Straight RAW conversion in Capture One in faithful pict style, so as it comes essentially.
Straight out of the camera, no 10 stop filter on this, RAW converted neutrally again.
This one with the 10 stopper, so you can see the brown cast.
While the screw in is probably more of a pain that drop in, you don't get the problem Dave experienced with light bleed at the edges. So like all things life is a compromise.
So I hope this gives you a bit more information to complement to Dave's excellent post