I think that the only cons I have seen is: 1) you have to flush the rock out really well every now and then to get rid of excess fertilizer build-up. 2) You have to water more often. 3) when you first pot an orchid into it, you often need to stake the orchid so the sharp edges of the rock don't harm the roots. 4) When reusing the lava rock, I have learned to boil it in distilled water as I have softened tap water.
I have been using it for a number of years, alone, and it has worked very well for me. Recently, I have added the new medium of LECA so some of my newer orchids are in that. Same concept.
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