From the Swapmixer link posted by @Coyster:
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Step 4. Write your review on the announcement thread. It must be more than 125 characters. (Review about your experience, how easy it was, speed, etc). Include your BTC address.
UniJoin rules:
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- Write constructive review and your suggestions in their
ANN thread within the next 4 weeks (deadline will be given on the next post).
In Swapmixer, their ANN has not been taken down and I don't recall anyone getting banned temporarily for posting their reviews. It is safe to assume that what they did wasn't against the forum rules. The same treatment should be applied to UniJoin which has similar rules. No, not in violation.