Ortho foam vs. IMF isn't a correct comparison.
IMF is a one piece foam that can be made of many different materials/combinations.
Ortho foam in gloves is an inner layer (so one of the layers of the sandwich) of foam used in gloves with layered padding (probably it could be glued to IMF either, but it would be wierd a bit imo). Basically it provides a snug fit and a very good shock absorption/distribution. And with layered gloves unlike with IMF you get a more flat striking surface once broken in.
It's a sort of personal preference. Some people love IMF in general, some only particular IMF (by particular brands and in particular densities), some don't like IMF in at all.
Some people hate the snug fit ortho foam provides (don't know why cause I really like it).