Having fitted winglets to my Mosquito some years ago I can say
there is (i) a small increase in climb rate (ii) possibly better l/d
and (iii) a definite improvement in handling.
For example, the left wing would drop at stall before, now it
stalls evenly. Also the handling at higher flap settings is vastly
improved.

On BGA handicapping, this amounts to a 1% performance
increase overall.

However...
- we spent 11 whole days getting them on straight and true

- the original kit was jigged incorrectly and would have resulted
in misalignment (food for thought when done professionally)

- the foil profile did not match the wing at the join. This was
corrected with re-fairing when the glider was refinished in Poland

Was it worth doing? Absobloodylutely!

bwBB




My Discus CS had factory fitted winglets.

However the "Cut line" between wing & winglet wasn't as per
the details
in the Schempp modification. (I assume the factory use a jig)

This lead me to have doubts as to the correct AoA of the
winglet, so I
stopped using them (After about 5 years!)

In general use I found there to be no difference with or
without, so I
continued to fly without them and didn't take the hit on the
increased
handicap.

I never found an effective way of measuring what the toe
in/out of the
winglet was, or figures for what it should be.

In summary, correctly fitted winglets may make an
improvement but it's
easier to make things worse than to make things better

PF