Experiences with rack mounted kit mounted *vertically*

Anyone have any long-term experiences regarding (wall) mounting
rack mountable kit front-down or front-up?  Reliability,
accessibility, etc.  And, any suggestions to protect the
openings-susceptible-to-gravitational-interference?
Any suggestions as to which (-up or -down) might be better?
For a start, I'd like to mount six 48/52-port switches.
Most of the mounting kits suggest this is within their
typical weight limits.  But, 4U seems to be the most common
arrangement (I'd like to have to avoid using two kits)