Make sure to ask where to go at the booth where you pay to park-they'll direct you to the proper area. Otherwise, if you follow the crowd to where everyone is parking it may not be possible to get to the diamond lot! It is NOT worth it at MK. At all. Epcot and AK are pretty good. MGM is good assuming they've finished the construction in the lot. Otherwise it's no better than regular parking. You just put it in your dash and don't give it away. You still have to pay for parking (unless you're onsite or have an AP) but it does get you closer. We stopped using it except for epcot and AK though. The lots do usually fill up around midday and it's not possible to find another spot in that lot. I would only use it in the mornings. We used them and found them mildly helpful, but if you left it at home, it's certainly nothing to be upset about.