They are forcing people to ride it to see the Giraffes/Rhinos/etc "up close"... But it won't be slow moving unless there's an animal in the way, these are proper HUGE Diesel (I guess) Jeeps, not on a track or whatever...
It's a Safari though, all you have to do is look at how well received Disney's is (Animal Kingdom) to see that there is a market for it, and it's all part of their bringing Zoo and Park together ideas... It's an unique point for the British public and the addition of the 'finale' section shows that they are willing to add a little extra onto the attraction, hopefully bringing a story full circle...
Been 5 years in the making this... I think the finale will make or break it...