Yep- the new FP+/
MDE totally drives me crazy. I hated it. I do plan. I pick which parks which days and plan 1 ADR a day (sometimes 2 for a day of the trip, if we decide to do a breakfast and then dinner, or have an extra restaurant we want to fit in). I also previously planned which ride I wanted to make a beeline for to get fast passes 1st thing in the morning (TSM, Soarin, Peter Pan). That's fine and I don't mind it at all. This planning a ride schedule in advance beyond the first FP we normally get in a day absolutely stinks. We go to WDW at least once a year (or we did before FP+- now that is in question) and I spent 3 hours trying to tweak the times so that we wouldn't be criss-crossing the park based on where I thought I would be during certain times of the day. It totally didn't work. FP+ kept us tied to the phone, was stressful, and made us criss-cross the parks and lose time. Trying to change FP+ while in the parks was next to impossible- MDE rarely worked for that, and when it did you would get messages that there were no times available for a ride you could walk to and pick up a regular FP that kicked in 40 minutes later. It stunk and we used it at a time when there was not yet tiering and regular FP was still available. The tiering and lack of regular FP, is why we have not booked a trip yet for 2014, and why it is doubtful we will do so. The direction WDW is going, it is going to be much worse for our next trip. It was really nice for the 1st FP of the day we usually get. I would set that one at 10:00 a.m., then I wouldn't stress if we were running late in the morning and when we got there, we would just go do things in that area until the FP+ kicked in. That worked well. Aside from that, our regular way of doing the parks, is that we generally go to an area, check the headliner- if the line isn't too long, we ride standby- If there is a FP that kicks in within an hour or hour and a half and the line is over 20 minutes, we grab a FP, then do everything else in that area until it kicks in. We then ride, finish up the area if we have not, and move on to the next park area. We don't go in hugely crowded times, so most rides this was not a problem, and it was very efficient. Now with FP+, we felt like we wasted a bunch of time running back and forth, left areas unfinished, and I sure felt my shopping time was pulverized as I rarely had time to browse the shops before having to run to another area. I will say that we really liked the magic bands themselves- and that says a lot because DH and DD normally absolutely hate wristbands.
We only have one kid. I expect for families with multiple kids who have different favorites the tiers are a nightmare. For example, how about a single parent with a one kid who loves Soarin and one that loves TT but either neither is old enough or is too scared to ride alone. You can't FP+ both rides. So, even if each kid only FP+ one of them, the parent can not FP+ both- not that they would leave one kid standing there. One kids favorite has to be picked for FP+, and the other kid gets left out. In a 2 parent family, the parents could split up- but if one kid likes both- they are left out in the cold on one of the 2 rides, unless the family agrees to split up again for someone to stand in line for an hour or more, or the whole family decides it is worth it to wait again.
It also would have been awful for us when DD was little. DD was obsessed with Peter Pan when she was little, when one FP for it was used, we got another-- we would FP that one probably 4 times in a day. If she didn't get multiple rides on that- it wasn't a good MK day for her.

Other than maybe 1 FP for Pooh, that was it. We didn't FP any of the headliners. Now- she wouldn't be able to ride it more than once unless we stood in the long line over and over.
FP+ really stinks.
That said- it may stink, but it isn't going anywhere, so OP I think you are going to have to use it if the 11 year old wants to ride any headliners without huge lines. The system is user intuitive for initially setting up 3 ( on their schedule, not yours) and you will easily figure it out as it guides you through- but tweaking can take some time- it isn't hard to do and it is user intuitive as long as you are aware you can move one at a time- it is just very glitchy and involves moving things around like a puzzle to get times to come up. Just know to set 3, and then go in and change them 1 by 1, to the times you want and that you have to move things out of the way, to get other times to appear. Some people recommend that if you want morning and afternoon times, to pick the evening schedule it proposes for you- that way you can move them indidividually without having to shuffle things out of the way. Also- if you want a parade or nightime show (illuminations/fireworks), you have to have a FP+ set in that time slot or it won't come up as an option. Go ahead and set the FP+. Just because you have them set doesn't mean to have to use them- but you may very well wind up doing so due to the line lengths when you are there. By the time of your trip, they might have MDE working much better in the parks so that you can make some changes while there- but based on our experience, I wouldn't count on that and I would initially pick times you think may work for you.