1) left/right controls are rather small
2) left/right controls are currently invisible when touch is enabled, on new Windows touch enabled laptops, this may cause:
a) controls sometimes disappear when using the laptop as a normal laptop
b) windows does not change between tablet and desktop mode until web page is closed [amazing "design" "feature" by Microsoft but apparently true]
Even on a small mobile device, a visual indication that it is possible to advance or go back may be better than no indication at all.
This is all mitigated if the solution to show thumbnails at the bottom of the next/previous images.