As you may already be aware, these were made in two batches some time apart. The later versions are greatly superior to the earlier offerings, so much so that I would advise against purchasing an example of the original version .
One way of telling the versions apart is to examine the cranks. Early ones are made from fairly thin pressed steel and retained on the axles by push in plastic pins with a hexagon head. Later ones have more substantial cast cranks retained by metal hexagonal headed screws.