EPDM best for flat roofs with no details
Kemper best for roofs with details ( we now use Triflex basically the same as Kemper but can be laid in colder weather )
EPDM is cheaper and quick to lay
Kemper or Triflex more expensive to buy More expensive to lay but bullet-proof as now joints.
Think logically If the flat roof has lots of skylights pipes and items on the roof that need dressing around, you have to cut and repair the sheet EPDM the more you do the more chance for a problem somewhere along the line
Look at this muck-up of a detail using EPDM
This is also true of all the sheet roofing materials look at this TPO roofing material again only 2 years old but the problem is with making good joints with details.