I've ridden the Shimano 4sp version (replaced by the SA 8sp). It rides a little flexibly but goes surprisingly well if you 'go with the flow'. Some funny creaks though, particularly when standing.
Adjusting the SA8 isn't hard (aligning between marks on the fulcrum arm in the 'correct gear'), although cable tension is quite sensitive (otherwise you get random gears).
Folding it (from memory) involves turning the handlebars through 180 degrees (the correct way to avoid damaging the front brake cable), pushing the saddle forward a little and lifting until the BB is near the top tube. The spring-loaded sleeve on the seat tube is lifted and the saddle allowed to fold beside the folded frame. The handlebars are folded either side of the folded frame. You end up with a long, skinny package (like a golf bag) that can be trolleyed on the front wheel.
There is a better folding description (and ride report and photos) on the Folding Society website.