You'd probably feel a lot better by
Giving the phones away.
Seriously,they're only giving $120 for the FLEX,so,don't expect much of a difference for the Z Ultra & next to nothing for the F6.
The above is for trade-in,not JUMP.Two totally different animals,but,the value (of the trade-in) is applied to the purchase of the new device.
In other words,you can't get JUMP value (balance on financed handset) on a non-JUMP phone.
Example:
LG G-FLEX non JUMP:
Trade-in value:$120
Apply towards purchase/down payment
LG G-FLEX bought on JUMP & JUMPING to the G3:
1) Outstanding balance is $0 w/trade-in of G-FLEX
2) Down payment (if applicable) towards G3
3) Monthly payments begin 1-2 billing cycles after getting new device.
4) Lather,rinse,repeat
There's some language regarding 6 months blah,blah,blah...... as long as you're willing to ensure the 50% threshold is met,you can JUMP as frequently as you wish. (In-store this is true,done it myself.On-line,YMMV)