Just did a bunch of research on this myself and going for the Superfly. You're correct...Superfly has permanent doors and the MJ does not but can be added for $75 which brings the total MJ w/doors price to $165 (sale going on right now) compared to the Superfly sale price of $110.
Superfly = 19 oz.
The MJ = 13.5 oz. (a 5.5 oz difference) but jumps to a total of 21.5 oz. with the added doors which puts the MJ w/doors 2.5 oz heavier than the Superfly.
When not using the Superfly doors they can be folded back out of the way such as shown here:
http://www.warbonnetoutdoors.com/gal...&g2_itemId=148
For me and my purposes, the Superfly was a no-brainer @ the sale price of $110 (regular $130)