I have bought them because I have tested one. It was giving 48 mhs for Ethereum and had a consumption of 100W. For me it was interesting and since it worked with one gpu, I guessed it will work with more. I didn;t even think that it will not work in the PCIE x1 slot...
To be honest, I think you might be able to mine Cryptonight coins more profitably than Ethash... If HBM is only half as good as HBM2 you'll should still get more than decent hashrates on XMR & co now that the potential's been unleashed by miners like STAK or Cast.
I will definitely try to get the best from it. First I have to figure out how to put more of these to work together on a rig