Hey, Dan!
I just bought the lens, and as I had one of the Heavy2star screw-in hoods for my 35/2.5, I wanted to see if it would do the job on the 21. More than just the flare control, I need a bigger hood to keep my finger(s) from intruding into the picture. With the supplied hood, even on the 35, I regularly take pictures of my fingers!
Actually, I had something like a dozen shots with the circular format. I cropped some of them, left a few alone...
If I run across an LH1 hood at a reasonable price, I'll probably grab it, but in the meantime, I've ordered a wider one from Heavy2star.
Regards!
Don