I fitted this to my 2007 GPS Corvette that already had a Tedur JAN-III on it. The fitting was easy enough - I just had to make sure the seat was clear of any existing glue and that the part of the headstock that the base seats on was exactly a right-angle to the top end of the fretboard, so be prepared to do a little work if yours needs doing this as well and only do if you're confident doing this kind of work. You don't want to make a mess of it.
Also, when fitting, be very, VERY sparing with the amount of glue you put on the base of the nut. I put on a tiny amount, yet there was enough for some surplus to come out around the edges. Also be aware that loctite superglue sets FAST. Make sure your nut is in exactly the right place before setting it down, otherwise you'll have a mess on your hands!
Once on, I noticed an immediate difference to the Tedur JAN in that the top part of the nut doesn't sit parallel to the base, it rocks forwards or backwards until the strings sit completely parallel in the grooves. In my case this meant that the top part of the JAN rocked forward towards the fretboard and sat at about a 5-10 angle to the base. I initially thought this was a fault and sent some pictures to Warwick, who were quick to respond and let me know it was normal. Since then, I've seen Andy Irvine playing with his brass JAN-III and his is the same. Phew!
Anyway, after all that, it is on and... the brass JAN-III is just ridiculously good. Like all JAN's it means you get another level of adjustability with your nut, all without filing or permanent change. However, what is really noticeable and the main benefit is the sustain it gives. A open string will just ring for ages and sounds so open and clear, really complimenting that Warwick sound and further brings out that low end growl. The way it rings out is piano-esque in it's nature. Plus it matches my bell-brass frets and looks the business.
It is expensive, but if you love your Warwick, it is a worthwhile investment.