The Notion Ink Adam has been "coming soon now" for a very long time. A few tech bloggers have tried it...but they tried older prototypes, and the Adam still hasn't come out.
If you don't need the iPad right away, you can wait. Here's the thing though: you can go try out an iPad right now. You can try out a Galaxy Tab right now. You can't try an Adam and I don't think they have a firm shipping date.
CES (a gigantic tech industry tradeshow) is coming in January. LOTS of new tablet products, designed to compete with the iPad and mostly based on Android OS will be debuting. You will have many more tablets to choose from after January, some of them possibly shipping within a few months.
The only benefit I've read about the Notion Ink Adam is that it has the Pixel QI screen, so you can read it in full daylight. Personally, I'm not impressed. (Of course, I can't sit in full sunlight anyhow.)