I am still relatively new at kayak building as I just finished my 3rd one. I have installed Etienne Muller's retractable skeg on two boats. They came out great and they work great but . . . a lot of work. I have seen keel strips mentioned here from time .The end game being, if a keel strip will give me the directional stability that would keep a recreational paddler happy.
Thank you for your sage advice and opinions :)

It is more about how much paddling has been done to understand the value of skegs,rudders,keels etc.the value of an adjustable Skeg is how it can CHANGE the yawing characteristics .Yawing could be described as "how playfull "or how much your ability(skill) to paddle a straight course you may need or your wish to spin her bow into /away from that rogue cresting wave.A boat that is designed to"track"won't be so cost benefiting for a Skeg or a keel because ,effectively, it (she)has something that does the same job and you're STUCK with it(her).However,to have a boat that suits both a playfull mood and be able to "go back home" in a sensible direction is worth the effort of fitting a Skeg or err,hmmm rudder,maybe...imho.It is far better to force yourself,if you are willing,to master this type of craft by refining your skills.A drop down/lift up Skeg allows for this ,safely,but only if you happen to have chosen to build a playfull boat in the first place.
Then,there is the situation of being exposed to "more"wind and a drop down Skeg can exploit the situation called "cocking"(wether,neutral or lee) very useful for changing how a boat is blown across the water by the wind and how the course can be helped by adjusting how much Skeg is being used.
Borderline sage advice but definitely my opinion.
All the best from Paul.