There might be problems if you have minor light intensity but in the same conditions I certainly do not want to read on a Kindle or paperback book either.
Either way the comparison with an careful selected 'extra white' paper with the JetBook Color is not an objective one.
Compare it with a newspaper (e.g. the Financial Times) and you're comparison would be quite different. I do not know many people who would say newspapers are too dark.
Anyway, I still think this comparison is not purposeful. Either you do like the eInk technology or you could just stfu and buy an iPad to play with 'angry birds'.