I agree that it's a reasonable amount, but I disagree that it's not a fee. My concern is that there's nothing to let me know this when I signed up. If I hadn't done some exploring, I wouldn't have found this.
Since I now know there's a way to unsubscribe, I feel more ok about it, and will stick with it, but if I can suggest two additions: one, that upon signing up, there's a notification that the upvoting thing will happen. Two, that there be a link on the page for unsubscribing to the service.