In processing a roll of FP4 reversal last night, I realised that I'd not noted down the second exposure time in my intructions. This is in fact 3 mins per side whilst rotating the reel under water.
I should also have noted that it's a good idea not to wear any clothes that you value, as potassium permanganate leaves a brown stain that is impossible to remove!
Another observation is that I've not found using filters to try to enhance clouds to be very successful, as they tend to give an overall mudiness. A pale yellow helps a little, but I certainly wouldn;t use orange with this film/process. However, the process does seem to render cloluds and dramatic skies very effectively anyway.
Finally, whilst I'd say that the success rate percentage-wise is probably comparable with shooting colour transparencies.
Finally (OK, I've already said that but here goes) as with colour transparency film decent light makes a world of difference to the end result.