Hello Tero,
on my 40Eperf I carry a Gennaker with a sock that came with the boat when I bought it, and since last year I invested also a (large) Code 0, cut for upwind sailing.
When I bought the C0 my sailmaker warned me that I would stop using the Gennaker once mounted the C0 which I doubted…
I sail in the Mediterrenean where often winds are very light, and sail as of 4 to 5 knots wind.
On my last trip around Sicily with large tacks off wind I did a practical test and furled in the C0, than did the hassle of deploying the Gennaker/sock and that was quite dilusive: with the Gennaker a could not bear at all any further off wind than with the C0 or it would stall/fall-in behind the Mainsail, at around 140degrees
I deploy both from the anchor roller tip like Neil does.
I took down again the Gennaker and continued with the C0.
My sailmaker was right.
My advice to you is to only buy a good quality and easy furling C0 that you use downwind as well as upwind.
Happy sailing and wish you good winds
Peter