If you to have the Fly more you do not need the Sling, I just traveled a couple weeks in Mexico with my flymore and the included case was perfect. Before I left I ordered and tried 6 different Slings including the 150 and 250. I was looking for a better option to carry the mavic, my Osmo Plus as my A6000, while it all fit snugly in the Sling 150 I sent them all back, it was just too easy for me to carry the mavic and the osmo in their stock cases without the bulk of the Sling. Especially in a tropical climate, whereas the Sling would have been uncomfortible in the heat as well it is far more bulky than the stock less inconspicuous cases.
regarding the 150 and 250 basically the 250 has a bigger upper compartment. Personally I did not like the fit of the mavic in either the 150 or 250, the adjustable dividers are very limited and it is not a good fit. I tried putting the mavic and the controller in the top un divided compartment of the 150 and that was a good fit but you need a cushion between the mavic and the controller. Again if you have the flymore case stay with it. the only thing it will not hold is the charger which you do not need while flying anyway,
I have a huge targus back pack I travel with and all my cameras and other personal stuff fits in thier stock cases and then I just take out what I need and carry those around, it was so much better than a ONE dedicated camera bag, SO in the main back pack I carry mavic, osmo, 2 still camera, all chargers, Laptop, 2 ipads, Ipad mini, portable hard drive (to transfer media to) and I still have 1/4 of the back pack left for personal crap when traveling.
When I travels at most when I went out to fly I took the mavic and batteries and the osmo or a still camera both in thier compact cases instead of a larger case.
regarding the 150 and 250 basically the 250 has a bigger upper compartment. Personally I did not like the fit of the mavic in either the 150 or 250, the adjustable dividers are very limited and it is not a good fit. I tried putting the mavic and the controller in the top un divided compartment of the 150 and that was a good fit but you need a cushion between the mavic and the controller. Again if you have the flymore case stay with it. the only thing it will not hold is the charger which you do not need while flying anyway,
I have a huge targus back pack I travel with and all my cameras and other personal stuff fits in thier stock cases and then I just take out what I need and carry those around, it was so much better than a ONE dedicated camera bag, SO in the main back pack I carry mavic, osmo, 2 still camera, all chargers, Laptop, 2 ipads, Ipad mini, portable hard drive (to transfer media to) and I still have 1/4 of the back pack left for personal crap when traveling.
When I travels at most when I went out to fly I took the mavic and batteries and the osmo or a still camera both in thier compact cases instead of a larger case.