Pre-Book Taxi Naples to Pompeii?

My wife has limited walking ability, so she wants to save as much energy as she can for Pompeii itself (Piazza Anfiteatro entrance), and not spend all her energy walking from the cruise ship to the train station, train station to entrance, etc.

So we are looking at a taxi from the ship to Pompeii, waiting for us for four hours or so (so she can take it slowly) then take us back.

I've found a taxi company that offers what we want for EUR 105, which seems pretty good to me. Has anyone used them?

http://www.taxiairportpickup.com/pompeii-limousine-taxi-van/book-transfer-from-pompeii.html

Is it a good idea or a bad idea to pre-book the taxi?

Thanks!