We did the shorter tour, English Tea Garden Presented by Twinings of London, which was very interesting - and fun. They take you around the garden and explain a history of Twinings tea, beginning with black tea and building from there. There were only 6 people total in our group, so it was very nice to be able to ask the CM's from the UK pretty specific questions about tea - they were very pleasant and knowledgable.
The Royal Tea Garden tour is longer, and happens before World Showcase is open. There is a fee, but it's 45 minutes long, and you get tea and scones at the end. For the above tour, they did give us some tea bag samples.