I didn't use the relocation bracket that came with mine. When they were on order I assumed they had to be relocated but the racks clear them were they are so I didn't bother going to the extra work as well as having the extension wires showing. They are still totally visible from behind....You can see my bike with Givi E-21s in this thread from when I first bought my Versys.
I decided to go with the 21s for the narrower width, as you mentioned. Plus half the cost of the V35s. I also like the top-loading feature. They have been totally waterproof. Also, once I didn't latch the lid correctly and I rode several miles before noticing that the top had bounced open. No big deal. With a side-loading bag, my delicate underthings would have been scattered over miles of highway.
Lots of other threads with good info on here if you search.
Also, in the photo in the thread above, I used the Givi turn signal relocation brackets. Later, I borrowed someone else's idea (can't remember who, now) and bought the KLR650 rear turn signals, which fit inside the boxes and eliminate the need for relocation brackets, extended wiring, etc. Neater installation. The turn signals are the only part of the installation that isn't utterly simple.
@Gustavo: The mounts for the E31s work with all the other Givi bags but NOT with the V35s, which are the Givi/Kawasaki ones.