Purchased the 12cm Opinel Carbon to use as a steak knife (plan is to get 6 of them total). It doesn't have the best feel in hand as a steak knife as it is a bit too big for that - and in fairness is not made to be one. However it makes for a great conversation piece and is unique enough.
Out of box sharpness is ok, but it really shines if you put it to a stone or two. The carbon blade is not too reactive - a patina did start forming early on but nothing to worry about.
The mechanism to lock the knife worries me a little bit as water can easily accumulate there and possibly cause rust, but long term use will show.
Overall, a very fun and unique knife to own!