Hi Pearse, cool that your system is going good! I use the same Yongnuo transceivers and they are working pretty good so far. You get 1 that doesn't work correctly every 15 or 20 of them but for the price, you cant beat that.
As for the clamps, I used some of those and I didn't like the strength of the clamping and they started slowly slipping down.
I do have however have the ones that you are using on the top of the stands but I have them holding with superclamps on the sides of the stands and they are super strong and it is the cheapest you can do for a setup that solid.
Leo