Just got back from a 1 week stay... ended up using Genie + at all parks, but only $LL for FOP and Rise.
We did not pre-purchase Genie, but then had a glitch in my app all week where I could not purchase Genie+ prior to 7 am. The "purchase genie" button would not work. However, once it turned 7am and I could make LL selections, it would let me purchase genie + through those screens. So an FYI if people are having issues.
The first day I didn't know that would work so I tried chat which made me call and then it was a 20 minute wait to talk to someone... but about 10 minutes in I tried to book and LL since I was sick of sitting on hold and it worked. I never got the issue fixed (I had reinstalled the app and downloaded it onto a different device with the same problem across the board) My app was glitchy all week- stupid stuff like the tip board would only say epcot and then halfway through the week it would default to MK instead, so I had to change park every time I pulled up the tip board.
We did get a lot of use out of G+, though didn't try for slinky dog, and didn't need any super early times for anything.
No issues with $LL jumping times for FOP or Rise.