I'm still on WT-4 so not much of an issue, it can't be used together ie: loose, or totally cannot mount onto the camera?
It's pretty sturdy IMHO.
the bottom mount, there is a slot so the L plate can slide out to accomodate the WT5, the slot is slightly shallow, so when securing will press against the WT5 too tightly. I heard the RRS one is ok but the price is really out there. Still checking if the Kangrinpoche one is ok.