I have an S520EX & an '87 Ibanez 540p power.
The ZR trem is superb. Without doubt it's the best Floyd Rose adaptation yet. The neck is fast as f***. The lighweight slim body is really comfortable - the only bother is that the strap tends to overlap to the front of the guitar which is a bit of an irritation during gigs. Soundwise it ain't a Les Paul so don't expect lush sustain... it's a mahogony body, but very thin. There are a few noticeable 'dead spots' and 'high spots' through the tonal range which are probably down to the limited resonance form the skinny body. INF1 & INF2 pups are ok, but I'm planning an upgrade to Holy Divers. I find the volume pot to be a little far forward for my liking. There are no position markers on the fingerboard, just on the top edge binding on the neck which took a while to get used to.
I bought the guitar as a backup, but I'm finding that I am using it more and more. We play a 3 hour set so a lightweight guitar makes life a litte easier for an ageing rocker!
The S520EX ain't the top of the range by any means, so check out some of the Jap models, but I can't fault the fit and finish on my example.
Hope this helps.