I did all the work myself but I have the skills and equipment to do it but I wouldn't recommend it because of the time involved and because the price difference between the two models is less than the cost of the additional parts.
If you wanted to convert to a hub gear with more gears such as 8 or 11 then an I4 would be as good choice as an D9.
I would like to try converting either model to a triple chainring, I think it could be done quite cheaply.
Excellent choice of fold bike though, they are well built, compact and a fraction of the price of a more well known small wheeled folding bike. The Mezzo also has a much bigger and more useful rear rack for touring. My dual drive mezzo with bull bars and Kojak tyres is quick and efficient.

Good luck.[/QUOTE]

Many thanks Guys,

Given that I have little experience of working on bikes I think that I will pay the extra for a D9. I'm sure I will be back for more information later.

Dexterdobe