They guaranteed me on a Ticker answer that every valuable feedback sent there is posteriorly evaluated.
However, receiving the monthly prize depends purely on luck. The more players sending Feedback, the more 30 days of Premium Time is sent, according to an information confirmed by a Customer Support member on a Ticket:
Thank you for your request. By giving valuable feedback, you have the chance to win 30 days of Premium Time. The number of Premium Times that will be given away depends on the number of all valuable entries. If you win or not depends on luck, the winners are chosen randomly from all players who have submitted feedback.
Tibia Customer Support
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