What is the difference between the scanners you offer

You can check www.socketmobile.com for more specific information, but here are the basic differences

M: Mid range, class one laser scanner. This one is fine and should work in most cases. We recommend
P: class two laser scanner. Suppose better than M under strong day light or hard to read barcode. I did not do any testing on those, so do not know the difference worth the notice between M and P

5M, 5P are scanners insert into CF slot.
7M and 7P are Bluetooth scanners