Why has Boeing used mini winglets on the 737-200?
When originally Richard Whitcomb of NASA developed the winglets, he developed the split winglets with one above and one below as shows in image below:

The one above starts at 0.4x chord from the leading edge. For a test program on KC-135 tanker, which I suppose was first application of the winglets, they used the type of winglets shown in the question:

Conceptually there is no difference in the &quot;mini-winglets&quot; and the &quot;Blended winglets&quot; While I think almost all the wingtip shapes are more or less of same efficacy, I can think of couple of reasons for variations seen among various aircrafts - One is patents taken for some shapes would force other OEMs to come up with different shapes. Second is weight of the wingtip vis-à-vis the reduction in fuel burn. Typically winglets reduce fuel burn by ~3-8% but in some cases, the increased weight can off-set majority of the fuel burn or even prove to be more than compensating for it, especially on shorter hauls. One may be able to make a lighter blended winglet using co-bonded, co-cured composite structure as compared to the short winglet mentioned in the picture which with say bolted joints might end up heavier. I think it would be difficult to say make any generalised comment on this.