J.K. Rowling

Yes..it is quite the experience though small and quaint. Quite the tourist attraction with long wait times sometimes.
The elaborate staircase in the center of the is reminiscent of the Hogwarts stairs. When we were there (Sept 2017) the University of Porto students were everywhere wearing Hogwarts style robes "welcoming " the new students.

I visited in November last year. No waiting line. The fee to get in was 5 Euro I think which can be used as a credit towards a book. Livraria Lello. I didn't want to leave. Great little bookstore and I've never seen stairs like that.

if you are an HP fan this is a must see in Porto (age 62 here, was there in early May). Go early and the line isn't too bad. Yes your entry fee can be applied to a book purchase (not a "souvenir" purchase). And if you don't buy anything it's worth the ticket price. Was definitely crowded inside but very fun. Doesn't take long to wander around (we maybe spent 1/2 hour max there).