We have a P8 and they are great! When empty you can turn them round by hand if you are rubbish at reversing trailers (like me!). Agree def would fit at least 8 big sheep, probably more. We've only taken 6 Shetlands in ours so far and they were rattling around in lots of space, probably could have taken 12!
If in good nick, sounds like a good price too, they are like hens teeth, we had to buy a nearly new one as couldnt find one at all a bit older.