Per Bill Tuthill:
I'm not sure about the purpose of the black paddle. Looks like a
sucky design. I bet it flutters in the water, because its sweet-spot
is high/far on the top, and low/near on the bottom.

They both work.

It's just that after a surf session with the white one, I always
come away with some sort of minor ding in one or both shoulders.

Werner's spiel for that one ("SideKick") talks about "...strong,
well conditioned..." users, so my assumption is that it's too
much paddle for Yours Truly - who paddles for hours at a time
against the clock with a wing paddle with no shoulder issues.

The black one ("Stkine") has less paddle area and is almost 3"
shorter (184 vs 191).

It's also foam construction - which makes balancing a surf ski
while sitting waiting for a wave in chop significantly easier...
you can just lay it in the water instead of having to constantly
scull to keep it on the surface.

In fact, now that I'm thinking about it, the shorter length and
floaty blade had as much weight in the decision to buy as the
shoulder issue - which could also just be a technique/surf
conditions thing.
--
PeteCresswell