I've had both CRG Lane-Splitters and Rizoma Reverse Retros on my bike. Actually, if you install the Rizomas so that the Mirror itself is on the inboard side, versus outboard...meaning the bulk of the mirror is over your hand, it actually won't make the bike wider. In fact, it'll be narrower than with the CRGs.
I had the CRGs, then wrecked my bike (not the mirror's fault). I replaced the CRGs with RRR mirrors. I couldn't be happier. I got the RRR BECAUSE they gave a narrower appearance. And, I find now that I have a better view behind me with the RRR. The CRG bar end (you know, the plug that fits into the end of the bar to which the mirror clamps) is far superior to the Rizoma, however. The CRG bar ends affix to the bars as if they were welded there. The Rizomas spin no matter how tight I wrench them.
Both are great. My personal preference simply is the Rizomas.