Depending on your family makeup, it is a definite perk.
I've used the morning ones and despite the "avoid it" mentality, I think you can get MORE than enough done in that first hour before the park opens to make up for any extra crowds later.
When I went to MK in 2015, we didn't try to rush in a lot of rides, but still got in 4 different rides (including multiple rides on the same ride) (after a leisurely stroll up main street, pictures, etc.) . .plus since you are already deep in the park at park opening the wait times from 9-10 am are pretty minimal as well.
We just went back to resort in the afternoon and avoided those crowds, came back for dinner and stayed until fireworks and I never found it "too crowded".
So while it is probably better to do with hoppers, it definitely isn't bad without if you KNOW the afternoon could be busy.
I found it so much a perk, my group is doing a throwaway room at Fort Wilderness so we can take advantage of EMH at Hollywood studios (not the only reason we got a throwaway room obviously) . It will help the boys can get first dibs at Jedi training and help avoid the issues of Tiering. My young family plans on just using EMH to hit all the rides at DHS and then hopping over to MK (where are fast passes are scheduled).