Edinburgh: Difference between "Hop on hop off" and Rabbie's version

Well on one, you have an experienced and knowledgeable guide taking you through the city sights and telling you about them and how they fit into Edinburgh historically, and on the other, you just get on and off at bus whenever it comes and go visit the sight that you want to see . . . then wait for the next bus and go to the next place, etc etc.

I didn't know Rabbies did an Edinburgh tour but they are a well established company and I would presume the tour is done over a set time.
With the HOHO tour there are several options and you do get guides with them though sometimes it is a live guide (I have a friend who is a guide on the buses) and sometime it is just a tape,you can get on and off the buses as you please spend a bit of time in one area and jump on the next bus to the next sight. buses run around every 15 minutes
http://edinburghtour.com/

FYI: I took the Hop On/Hop Off in May. 15 pounds, 80 minutes long. I didn't hop off. I just rode the loop and sat up top!