As pp said Express Pass comes with the three top tier hotels. Hotel guests at any level get early park entry. You can check the universal website to see which parks open early and when. I highly recommend the top tier hotels, (Royal Pacific is our favorite) because your entire party on the reservation can use the room key for express pass the day of check in AND day of check out—all day. The Express pass let’s you get in the shorter que, you don’t need to schedule anything like fast passes. Also, Hagrids is on virtual line, you need the app to get in the virtual line and that starts at park open. I have been able to get a virtual line time on the bus and while in line so you don’t need to be scanned in the park to do it, just close to the park. If you are already there at early entry it’s no big deal to hop on and get a time BUT on very busy days the times fill up fast. Sometimes on very busy days other rides may go on virtual line, so the app is important. Express pass can’t be used on virtual line rides (hagrids). Express pass CAN be used on hog warts express train that runs between parks (originally you couldn’t but they changed it). No spoilers but the train is very cool and not just a way to get from one park to the other. As pp said if HP fans you will want park to park tickets in order to ride it. Lastly, I’m not sure how often the people will go but for some it makes sense to get at least one annual pass to get the discounted hotel, discounts on food and park merch. Check the prices on park to park tickets then compare to passes (which are considerably cheaper than Disney passes), and see if it works for your party.
Edited: Because I wanted to add that sometimes hagrids will be on virtual line in the morning but then “go off” of virtual line if they decide it’s not too crowded (it’s annoying). We showed up once at our return time and were told there was an hour wait and I said but we have a virtual line time and they said they stopped the virtual line sign ups because crowds not that bad, I showed our phone with our return time (I screenshotted) and they said “ok then go” and let us go into a separate short line. So JUST in case that happens, I’d still suggest going at the return time given. There aren’t anything like magic bands to scan and you can wait in the regular line as many times as you want if they are not doing virtual line. Also you have to scan your room keys and tickets for express pass so we get lanyards.