With regard to whether Pairtrade Finder works, you can demo it for 30 days to experience the results for yourself. You can also purchase it now and get the 3 hour video course included and if you find it doesn't work for you then you can ask for a refund.
The owners and managers of Pairtrade Finder use the program and find that it works and that yes one can make money with it, but you do have to spend time learning just like with everything else.
As to what % you can earn from trading using it, that is a question that depends on risk-reward, entry and exit stretch levels, hedging levels, position sizing and many other factors. We are not a training company and we are not regulated to offer investment advice so we have to suggest that you explore other sources for an answer on that question.
PTF generates a signal when a pair is 2.70 (a entry level which can be configured, refer to User Manual) standard deviations away from its mean, which is essentially the ratio price of the 2 stocks, then measures the last 100 day average of the ratio, then measures the day to day change in the ratio. When the current ratio moves at least 2.70 standard deviations away from the 100 day average (the mean) a signal is generated. When the ratio moves back within 1.00 standard deviations of the mean an exit signal is generated. You can change these entry and exit standard deviation from the mean parameters in PTF. It may be helpful if you start paper trading PTF on some US pairs so you get a feel for pair trading in general as you will have to answer some questions about the trading strategies.