Ghwellsjr, I too believe that your test method is inconclusive. I use Hobbicolors PMT-BK very heavily too and it never clogged my print heads or cartridges. I don't know if there are actually two different inks under the label of PMT-BK. If there are so what? Image Specialist ink has had many changes over the years too. If the change is an improvement why do you need to be concerned? I would be concerned if the quality got worse or if the price become higher. You seem to have an attitude toward 3rd party ink brands except Image Specialist. IS is a 3rd party brand too and it had its share of problems too.
I refill all my BCI-3eBK, PGI-5BK and my lates PGI-220BK with Hobbicolors PMT-BK and I do not purge any of them on a regular basis. THey seem to work flawlessly without purging. It is a great ink that works just perfectly. You need to rethink how you judge the quality of ink. Most importantly don't bias your brain the way you think. You many not be aware that you are biased.
I refill all my BCI-3eBK, PGI-5BK and my lates PGI-220BK with Hobbicolors PMT-BK and I do not purge any of them on a regular basis. THey seem to work flawlessly without purging. It is a great ink that works just perfectly. You need to rethink how you judge the quality of ink. Most importantly don't bias your brain the way you think. You many not be aware that you are biased.