The two paid plans unlock the same features. The difference is how often you host and how you'd rather pay.
Side by side
Pick the Event Pass if
You're hosting one thing: a wedding, a milestone birthday, a reunion. You pay once, the event gets 25 GB (room for a 200-guest wedding, twice over) and video for about a year, and there's no subscription to remember to cancel. Hosting another next year? Buy another pass; they stack, each with its own year and storage. See how long an Event Pass lasts.
Pick Pro if
You host more than a couple of times a year, or one event will outgrow 25 GB: a photographer, a venue, a club, a family that documents everything. Unlimited events, a storage size you choose (50 GB, 200 GB, or 1 TB: a season of parties, a planner's year, a venue's year), and yearly billing at two months free. You can change size later from Change plan; a smaller size just has to hold what you store. See upgrade, downgrade, or cancel.
Moving between them
An Event Pass converts to Pro, prorated: the unused part of what you paid becomes credit against your next Pro invoices, so nothing is lost. The Pro size you pick has to hold what your passes store now; if stacked passes hold more than it does, you're shown how much before you pay. Pro holders can't buy a pass (Pro already covers it). When a pass ends and you don't renew, the account settles back to the free plan with a grace period for anything over its storage.
The features are identical
Nothing about the album, the guest experience, or the reel differs between Pro and the Event Pass. Choose on events and storage alone.