Anti Spam is free to download and offers filtering without paying a single penny. However, if you want to take full advantage of the last option and block (finally!) calls from the relevant numbers, you will have to opt for the paid version.
So there is no subscription, but you have to pay the amount of 4.99 euros to use the blocking feature. This automatically redirects callers (especially agitators) to voicemail in the same way that you manually block a number from your call log.