Is there any information on the accuracy of this indicator? 

Please, clarify how would you measure the "accuracy"? As many other indicators it shows you a kind of "overbought" (high probability of sell) and "oversold" (high probability of buy) states, and on stable market (without a high impact news) it performs great.

Will there be a demo version?

I can release a free version for a predefined symbol. Will this be ok?

The demo version is available now.

There is a complementing indicator - PriceProbabilities. It provides the same maths for invocation from expert advisers and visual analysis on history.

You can find further explanations of how the indicator works in my blog - Back To The Future: Part 1.

The new version 1.4 has been published. Except for bugfixes it provides 2 visual buffers with historical buy/sell marks and current state, which are accessible from expert advisers for automated trading.

Also the price is reduced.