I first noticed Robert Oster's ink on ebay and wasn't too sure about it. Then I saw someone here had taken the plunge before me and the ink seemed good, so I took the plunge and contacted him. Customer service was truly excellent; he always responded very promptly and politely and was very helpful. I got seven inks in one package by ordering directly from him. I can't give a full picture review here as all my photographs are too big, so I have a picture of a comparison sheet below, after my thoughts.
Moss Green: Very nice green with a slight grey aspect. Quite dark and a genuine 'moss' colour. No shading.
Orange: This one doesn't come out very well in the picture. It is very bright, no shading and is a little bit like a highlighter ink but is deep enough for normal use. It 'pops'.
Lime Green: Really lovely citrus green. Nice and bright with slight yellow hints underneath and a small bit of shading. It gives Kobe's lime a run for its money.
Royal Red: A standard red, but quite a nice one. No shading. Looks a little flat on Tomoe.
Barossa Grape: lovely murky purple. Very dark; perhaps a little like Ink of the Witch? I have nothing quite like it.
Deep Sea: really awesome. Like a slightly more saturated Emerald of Chivor. Nice shading and sheen. It has a tendency to bleed a tiny bit on Tomoe, but I had no problems on Clairefontaine or Rhodia.
Jade Green: Very nice murkey green, a touch lighter than Tanna Japonensis if you know that ink. Has shading and a slight brownish/yellow undertone.
I simply wanted to add that these inks are really great. They all have quite strong saturation and a wetness on the nib, good flow, decent lubrication, no staining issues (some of them wash out really easily) and reasonably fast dry times. Except for the Deep Sea on Tomoe I had no issues with show through, bleed or feathering. It's the deep saturation for me that makes them really attractive. I liked these inks so much that I'm already narrowing down my list for the next seven in a pack.