Pattern Keeper costs around 9 US dollars, as a one time charge
The trial version of Pattern Keeper is fully featured. This means that you can try everything before deciding to buy.
You can no longer open you charts but your data is kept safe!
Yes, if the devices use the same Google Play account you can use it without paying again.
There are plans to develop an iOS version of Pattern Keeper but there is currently not a set time frame for its release.