We did it. We booked an onsite room for the front of the line passes (it was cheaper than buying one day hopper tickets and paying for fotl passes separately - it was a saturday in july, front of the line passes were a necessity for us) and early entry but we didn't end up staying overnight. We had it in case we needed a midday break, or in case we were too tired to go back to the Wilderness Lodge at the end of the day. Instead, we started the day with our one hour early entry at 7am and went until around 5pm, then used uber to get us from Royal Pacific back to the WL. It was exhausting.
HERE is a link to the start of five posts in my trip report detailing how it went, if you're curious.
It was not a cheap day, lol, and we sandwiched it between an Epcot day and a day with a prepark opening breakfast at Tusker House for our Animal Kingdom day. But, it was also for my youngest son's 10th birthday (ok, and for ME, because I am HP obsessed!).
I'd like to go back again and take it more slowly, but you can hit the highlights of both parks in one day. They're very close together, and after WDW, it was almost surreal.
It's a totally different experience, in my opinion.
Good luck making your decision, and have fun!!