I ABSOLUTELY LOVE my EOS M! Great little camera.
I was looking on DxO Optics. The 22 mm kit lens on the EOS M - that costs $95 new on eBay - is as sharp as my Canon 24-70 2.8 II on my Canon T4i. Not bad for a $250 camera & lens combo!!
I have a Hoodman viewfinder that I use on my EOS M - same basic thing.
I have found, though, that by turning the LCD to full brightness, I can see it in full sunshine with no problem.
I tested it, turning fully around in a 360 degree circle. The only place I had trouble was when my face was fully lit my the sun, when my subject was backlit, for about 20 degrees of the arc. I could solve the problem just by tilting a ball cap down trp shade my face.
The rest of the time, I had no problem seeing the LCD with brightness all of the way up.
One tip: You can program the "Trash Can" button to increase the LCD to full brightness. Works great!
Otherwise I use the "Trash Can" button to change ISO. I put the Custom Function to select the mapping of that button on "My Menu."
I never need to change ISO in bright sunlight, so it works perfectly to switch that to the LCD brightness ...
Good tip! I'll try give this a try today.