I have owned both and can tell you the difference. The SBE is lighter and therefore is a little better for decoying doves, wood ducks, quail, etc. and the Extrema is heavier and therefore swings a little better and is better for longer shots like mallards, geese, crows, passing doves, etc. Both can be used for all the stuff I mentioned before, but it's kinda like golf clubs, or fishing rods.....one will be just a little better for each specific use. If you will be shooting lots of 3.5 inch magnums, get the Extrema....it kicks noticeably less with the magnums.
As far as cleaning goes, the SBE will take you about 10% of the time it will take you to clean the Extrema. Neither gun, however will need to be cleaned after you shoot every time. Try maybe after 500 shots or so. The barrels are chrome lined and there is nothing that will rust any time soon. That's why they cost so much.
Hope this helps.