I tend to prefer 6x6 as well - size does matter when it comes to negatives after all. However, there are times when 16 of a smaller negative are better than 12 of a larger one - for example multiple exposures. Negative size is less important then because you are not so interested in capturing the detail - just form & colour. Then having 16 shots/roll is better because you use fewer rolls of film. Normally for multiple exposures, I use my Holga 135 so I get 24 or 36 shots per film, but if I'm travelling I don't like lugging two film formats around so I usually take a Diana with me for multiple shots.
Anyway, I bought Rex because he's unusual, made from plastic and as Tintin said it's a neat camera and it'll be fun to use.