Philip,
I've got some experience with the brightscreen magnifiers and my feeling is you'll be disappointed. I have their product for the leica DMR, and two D3 magnifiers for hasselblad that I adapted to work with the Rollei. I simply don't use them. Many other camera makers such as mamiya produced much higher quality devices. The one for the RZ can be adapted to the AFi by a competent machine shop and give you much better results for less money than the cost of the brightscreen units which I think are really disappointing optically. I have not used any of the brightscreen focusing screens so can't comment on those but I have a Bill Maxwell screen in my Rollei and it did help some for focus. The thing that made the best improvement was using a chimney style finder instead of the prism as it gives you a 3X on the whole field. I really don't know if Rollei has one of these available for the AFi-10 or not but maybe the 6000 series could be adapted by changing the base plate out. You might write Reiner at DHW and ask him. If there isn't a viewfinder magnifier for the Hy6/AFi then you could see if he'd sell you the bottom plate for the prism and then any 6x6 loupe could be fit to the base by a competent shop. I have an assortment of these that I've made myself for my 6008 ranging from 3x to 5.5x for different tasks.
Eric
Thanks Eric. Yes, I think give the Brightscreen magnifier a miss and look for alternatives, including the RZ you mention. As for the brightscreen focusing screen, it's been ordered by my dealer in the UK who sold me the camera, at his expense as part of the deal. He was told they made them for leaf and as the temporary one in my camera has the wrong format masking lines he has agreed to get the right one. Also, the temporary one doesn't have either a split screen or micro prism and I find it very difficult to manual focus critically with it as the tolerance with the Afi II 10, with the short depth of field of it's massive sensor and it's 56 megs. And that's doing it slowly in tests, it'll be worse in the real world with speed.
However, I did try my old rollei screen with it's horizontal split and it was altogether better, so I've asked for the brightscreen to have a split and micro prism. If it turns out to be poor I'll contact rollei and ask them to do me theirs with the 56mm x 36mm masking lines.
I do have both the waist level (chimney) finder with the 3x magnifier and the leaf 45 degree finder, and the above experience was with using them! I have my old rollei x6 loupe but the rollei base for it will not (i don't think) fit the Afi camera. Maybe an adaptation would be possible.
Philip
ps. I replied to your message regarding the x-act.