You are correct, shot with the WO Z73/Flattener as listed in my signature. I have had the ZWO EFWmini (5 slot) in the mix, and experienced no issue with either focuser, or mount. The WO focuser seems very solid and able to handle a lot of gear. I feel that I've never even been close to its limit in any configuration I've had it (flattener, spacers, rotolock, EFW, camera). I even put a rather large/heavy flip mirror in there once, and while I couldn't reach focus because of the spacing, the focuser handled it just fine. Still, I know that many prefer to get a Moonlite, or other focuser. The only modification I've made is to attach the Sesto Senso robotic focuser.
I've used both the ASI294 and 224, with pixel sizes 4.63, and 3.75 respectively, in both cases the stars when greatly zoomed appear perfectly uniform and round to me, with equal number of pixels matching in the cardinal directions saturated to the same degree. I hope I've explained that correctly ... in any case, the stars look round to me, corner to corner. I interpret this to mean that both the flattener and the tracking/guiding are working very well.