You need to have a tax license to buy from image specialists (at least last time I bought from them). But, http://www.inkjetcarts.us/
sells there inks.
You can contact image specialists and they will send you sample prints.
The 3rd party inks I have used normally show more bronzing and gloss differential but I mainly print on matte paper so it is not an issue.
I will let you know that my 1st iPF5000 lasted a little over 2 years before needing printhead-hard to know if it was from the ink or not as they did not have good printheads to begin with. My current iPF5100 also went 2 years before printhead issues. This is harder to know if it is lack of use or the 3rd party inks.
My problem is I do most of my printing in November when I run about 1800 sheets through (1050 8x10 photo's and 750 of text), then VERY little use the rest of the year. So, if the cause of the printhead nozzle issue is from the inks then its hard to justify the cost savings. If the cause is lack of use then it is worth the cost savings.
Just unsure with the iPF5100 if it was lack of use or 3rd party inks to cause my most recent issue. My usage was 1700 sq. ft. in 742 days. Most of that was in the previous two Novembers.