The stock mirrors on the rex are great big piles of junk.  They work great if the only thing you want to see in them is your bicep, other than that you’re constantly twisting your head around or ducking and weaving trying to get some idea of what is behind you.  So I shopped around on e-bay and picked up a cheap pair of bar end mirrors to replace them with.  They aren’t too shabby for being $10 with free shipping, although the bolt was too short and I had spend half as much as the mirrors cost on two stainless replacements.  But once I got them on and adjusted I was able to get a pretty large field of view compared to the stock units.  Here is a side by side with the stock on the left and the new bar ends on the right.  The only thing I need to get used to is that I can’t just slide my hand off the end of the bars anymore.