no one but you knows if it is worth it for you. if you have a large group or do a lot of the rides with on-ride photos, or go to a lot of character meals/dinner shows with photos taken, it is more likely to be worthwhile. if it's a group of two or three and you are not doing these attractions/meals, it may not be. if you really just want the posed photos in front of the icons, you can have the photopass guy take your picture with his camera and then yours, and you can buy one or two pictures afterward from the photopass website.
if you buy through the disney website it is automatically linked to your account and to all people listed for that trip. then you can go on the website and give other people privleges and viewing rights for the MM package also.
all folks listed/linked will have all photos automatically linked during the rides, and they will scan one members magic band for all posed shots.
however............we have noticed that since so many people started buying the package before they go, the number of locations for photographers has decreased. used to be all over the parks, and some just roaming around looking to set you up for shots or get your family on a ride. now just mostly in front of the icons in each park. also, frequently on our trip this month, the ride linking was down and you had to stand in the line to get your pictures linked, sometimes 20 minutes!! this was annoying enough, but on one ride they didn't even have anyone at the exit telling us that. so we left without linking, but then using babyswap, the next group went right back and were informed and we were able to link the prior photo, so ask when you see your on-ride photos if it is working or not