Allan,
This thread is getting confusing but your photo shows jib cars. I started out with only a jib and cars like these. When I bought a genoa I tried using the jib cars for the genoa but it doesn't work very well. The cars need to swivel (yaw) to find their optimum position because a genoa sheet has to double back on itself to go to the winch, a jib sheet doesn't.
I have ended up with both spring swivel genoa cars AND Garhauer type EZ cleats ("Swivel cam cleats" - Kelly Hansen) The cleats work great for single handing in light to medium light conditions, but once the winds get up the loads increase dramatically. There are several on this site who swear this is no problem.... they just head up to reduce the loads and re-trim. This is true, but bear in mind these are guys who have ALREADY mastered Mac handling and are competent multi taskers. Because I'm a purist, I hate doing this, it irritates me to lose speed in order to re-trim . So I end up both feet braced on the opposite seat and both hands pulling for all I'm worth.... sore hands, sore shoulders. Plus, under high loads, I've had the cleats arms start to flex, and the sheet starts to slip put of the cleat and then let go....... WHAMO! sudden lose of drive, wildly flapping genoa, wildly flailing genoa sheet lashing seven shades of s@%t out of the admiral who doesn't seem to have the common sense to get out of the way

!! Sudden loss of the theapeutic value of a nice quiet afternoon's sail together

.
Here's my take.....
1. If you get just genoa cars, they will work in all conditions but will usually force you to use the winches, making single handing clumsy and awkward.
2. If you get just EZ cleats, you'll love single handing but may find it harder than you anticipated in stronger winds making you wish you'd got the cars, or forcing you to get them as well anyway.
3. If you had bought my boat, you'd have got jib cars, genoa cars, and EZ cleats ALL THREE

!!
Robin.