That looks like its a Mallossi Multivar. Probably one of the better variators out there, loads of folk say they are real good variators.
The spring will be a torque spring for the rear pulley, prob 1000rpm rated, gives you better uphill speed and acceleration after slowing down to go round bends etc. You need to check what weight rollers you get with it, stock weight is 6.5g rollers. Heavier than that will give you slower acceleration but maybe a little more top speed, lighter rollers do the opposite.