I feel like both vapenstone and mosh are both correct on this issue. I recently sold both my solos M107/M1D in preparation for a new vape but Here are my thoughts:
i prefered my pvhes stems over the eds stem (which ive only tried a couple time, never owned) also the pvhes stems with the travel tube filled with rubbing alchohol and some salt, clean the pvhes or any glass stems in a minute so they look brand new. It is soo much easier to clean a pvhes then the Eds so id feel much safer traveling with my pvhes.
On the other hand, Eds stems dont have to worry about breaking so their is an advantage there. Have broken pvhes stems while getting out of my car, another one rolled off my desk and broke, and a third one broke inside the travel tube while inside my bookbag somehow...so they are definately breakable
As far as airflow, both are probably correct. Every PVHES is a tweaked stock stem so some are wider and others are tighter. One of my straight PVHES is a wider one so its pretty tight, but it has the same airflow(maybe very slightly better) then my stock stem. My Turbo stem is about the same thickness as my stock stem and provides about the same airflow as Eds stem.
On the other hand, my original/broken straight PVHES and my shorty PVHES are slightly thinner and a lot looser (fits in and slides out without any resistance) both of these stems each had compareable airflow to the turbo and Eds stems. Basically no difference between my tighter turbo stem and the looser shorty and straight PVHES.
I think its a little harsh for mosh to say anyone who thinks PVHES provide better airflow doesnt know what they are talking about, because like i already mentioned no two stems are exactly the same so airflow will vary. If I had to guess i would assume that the stem that mosh was using was a tighter one, but i dont know for sure.
If i had to recommend one for someone to buy, i would definately recommend PVHES, however I would tell you to specify in checkout to request a looser fitting stem if your buying for airflow (unless your buying the shorty only for the smaller bowl size or a turbo then it doesnt really matter)