I just looked at the Stagg website and it looks like they have done some different things to their newer models. I think what you are asking is what the difference between geared and friction tuners. According to the stagg website their ukes now have geared tuners. Mine has friction tuners.
The gear(ed) tuners are more percise and alot of people find it easier to fine tune their ukes. The friction tuners can be a little difficult to use at first but once you can use these you will be able to tune anything. They work on the basis of what you turn is what the top turns the same amount. With the geared tuners what you turn on the tuner is proportinal to what the top turns.
Hope this helps.