I find these starters work really well if the parts are in serviceable condition.
The 2 friction washers and metal washers etc must be dry so cleaning parts with brake clean or thinners and even roughing up the old fiber washers with a file or sand paper helps.The spring can be stretched for more tension if loose.
When first pulling on the starter rope the 2 starter pawls must move side ways if not the starter will slip when starting and as Mf mentioned the 2 pawls must have a good edge (not worn) where they engage into the alloy cup.
Once the starter is right and as long as the starter cup isn't excessively worn the starter should work well.
