There's an article on Seeking Alpha that is specific to this ADR, it's used as a pump n dump frequently by day traders because the conversion isn't straightforward. A year or two ago I believe it was trading at 100% higher than Athens price, for instance. A lot of people buying into that and not bailing in time got burned.
Conversion works like this:
Take Athens price from ALPHA AT: 0.695 euros
Convert to USD: $0.96
Divide by 4: $0.24
Add $0.035 (ADR creation fee): = $0.0275
Anyone holding this above $0.0275 is being taken on a pump n dump. Enjoy the ride but be ready to bail out in time and don't even think of adding above that $0.275 price unless you want to lose a lot of money when it inevitably corrects.