The viewfinder is bright and always visible.
No reflex mirrors allow you to maintain sight of your subject at all times.
They don't have through-the-lens viewing.
Lack of a mirror makes it quiet and easy to hold steady when using slow shutter speeds
A TLR camera is viewed through the top from waist or chest level while SLR cameras are viewed at eye level.
A SLR camera is viewed through the top from waist or chest level while TLR cameras are viewed at eye level.
Nothing is different about viewing through a TLR or a SLR camera.
None of the above.