If you go to my gallery of images from Anilao, Philippines, the purple nudi, 3rd Row, 4th Column:
http://stewartsy.com/anilao-was-just-like-coming-home/
that was taken with the 7D, Canon 100 f2.8 Macro and the Aquatica +10. The nudi was about the size of a grain of rice. The image is about 75% of the original. IQ wise, there would be no difference really with the Subsee or Aquatica diopters. But the Aquatica close up holder is quite a bit cheaper than the Subsee holder and it's made to fit on both versions of the Aquatica Macro Port. The O-ring retaining system is very sturdy and there's no danger in the diopter falling out.
http://stewartsy.com/when-11-macro-isnt-close-enough/
Working distance with the +10 is about 2-3 inches from the subject.
Full disclosure, I am an Aquatica Dealer, but the prices I'm quoting are readily available by checking the website of both Aquatica and Subsee.
S.