TL;DR: Go on the tour but don't book through Viator. They gave us invalid tickets, wouldn't help us when we asked about it, and severely limited the time we'd have, after lying about it.
The WB Studio Tour is amazing, I just wish I had more time to explore, which brings me to the issue. The emails from Viator said I would receive tickets 1-2 days before my experience. I got an email saying my tickets were here, so I clicked the link in the email and it opened the app to a page that said "This is not your ticket". That's fine, the email mentioned that. I clicked the button that said "Download Ticket" and got a PDF that said "This is not your ticket". Curious, but probably just a glitch. There was another button that said "Send Tickets" so I clicked that and got another email that said "here are your tickets". Clicked the link "This is not your ticket"; clicked the ticket button "this is not your ticket". Finally, less than 12 hours before the experience, I got frustrated and called the 24-hour line and Tina answered the phone. Tina emailed the tickets to me. She said that someone had already mailed the tickets, but no one had. I got the email and opened the tickets with Tina on the line, but the times didn't line up. The bus ticket was 2 and half hours before the tour (the bus ride is less than an hour). Tina assured us that we would be able to go any time between 10am and 6pm (as per the WB website, but Viator only had scheduled tours). I asked about the scheduled time on our tickets and Tina said she'd look into that before hanging up on me.
The next morning, we run across town to get to the pick-up location, get to the bus, scan our ticket and it doesn't work. The attendant looks at his list and we're not on it. He carefully reads the ticket and we realize it wasn't two hours off. It was 26 hours off, the bus ticket and the attraction ticket were for two different days. Even though we had unused bus tickets and valid attraction tickets, both booked together through Viator, the attendant wouldn't let us on the bus. He decided to WhatsApp his supervisor (not call for some reason), and in waiting for a response, we missed the bus at our "scheduled" time. We had to take a bus half an hour later. We still got there over an hour before our scheduled entrance time, and THANK GOODNESS the nice people at WB let us in early. But the bus gave us a 4:45pm return time, assuring us that if we missed the bus, we'd have to find our own way back. So after Tina assured us that we would have up to 8 hours to go, explore, and come back, Viator made sure we had less than 5 hours for everything. We had to rush through the experience in fear that we couldn't get back to London.