Lurker:
You should also consider looking at the bar end mirror by Zefal. I have seen the mirror you're tlaking about at a local LBS. A couple months ago I was downtown riding to a meetup with some people and my current setup then was with one of those velco strap on/off round mirrors. While the round mirror was good on the view and very easy to adjust on the fly however it did add about 1/2 foot I'd say (probably shy less then 1/2 a foot) to the width of the bike making weaving in/out of tight spots hard. (my current mirror
http://www.mec.ca/Products/product_d...=1158569455075 ) I did however gentlely tap a cars mirror which I wrote a note explaining what happened and how to contact me to the driver even tho mark as not too noticeable at night. I felt it was the right thing to do.
Anyways, after that mirror setup I was thinking of getting something that would allow me to keep the same bike profile without anything poking out and was foldable and slimmer. BTW my old and stil current use mirror was foldable but still you had the bar extended out tho. So I walk into my local LBS and see this kitted up bike on display. A bike Mr.T would be happy with with all the tools and such on board. Anyways I check out the mirrors which are the one you're talking about and they seem ok but yes, they are narrow and I was not too sure on how the handbar end would hold up with the large open hole area there.
You might want to check out this Zefal model. Very similar to your narrow one you have right now.
http://www.zefal.com/AAA/produitFram...&languePage=an . This one I like for the extra view but not too large to put of the overall look of your bike. This model I know is a bar end mount. Also you have enough real estate to add a very small wide angle circle sticker mirror onto this model to check your blind spots like how some car drivers use.
Zefal makes two other mirrors. I'm starting to like the look of this one. Bar end top mount.
http://www.zefal.com/AAA/produitFram...&languePage=an could be useful as a secondary spotter seeing how that model allows versatile anywhere mounting. Tho I'm not sure if it's foldable.
The last of the Zefal model allows a slightly wider view and is also a bar end mount. It does look foldable.
http://www.zefal.com/AAA/produitFram...&languePage=an
Hope that helps some.
Zero_Enigma