Hi Charlie,
I have tried them for a short while (I wanted accuracy, so in the end I used the triple flanges from the ER4 XR). I have used the smaller ones to see if I could use them deeply inserted, but they are (predictably) wobbly in my ears, compared to the triple-flanges.
Shure foamies actually work (the small works again for deep insertion), but the larger size is meh. That also holds for the Shure silicone tips, which I used for quite some time on my Shure earphones before they (rightfully) died; they are technically fine, but not a success on the ER4.