I've recently installed a Remus exhaust on my F56 JCW + Milltek de-cat Downpipe, it sounds absolutely mental when open. It does, however, rasp a little bit when 100% opened. The exhaust itself is legal and should not give you any problems because it has an European certification (the Sound Controller does not, but the exhaust does). The de-cat downpipe is not legal, but nobody would care about it where I live.
If you are looking for a lot of sound and pops and bangs, you'd be better off with a de-cat downpipe. That isn't legal though and you can't control the sound. You'd have to drive with a loud car 24/7, which in my opinion is not really ideal.
I have no experience with a JCW Pro, but I'd imagine that this sounds great aswel. The JCW Pro does not give you the option to open the exhaust a bit, it has to be either open or closed.
Therefore, I'd say you are better off with a Remus if you want it to be approved in Spain and not have any problems with neighbours and police etc.
You should, however, go to a MINI meeting and just hear what the difference between the two really is.