Because of the lack of funding for both CITES and the national authorities, the actual number of such reviews is tiny.
Between 2010 and 2016, of the 40 species selected for Review of Significant Trade over the same period, only about half have been completed (either by uplisting the species to Appendix I, implementation of the recommendations by the country or by downgrading the category of concern). The other 20 reviews are still ongoing, meaning the concerns persist, and recommendations made to the country have not been fully implemented (be it through lack of funding or stalling tactics).
At this rate, the mechanism can never be effective given the increasing number of species listed.
Key is that the Review of Significant Trade is totally dependent on the quality of the trade data. Because CITES does not even mandate import permits for Appendix II listed species, the most basic reconciliation cannot be done.
The hippo was included in the Review of Significant Trade twice. Of the main exporters of hippo parts and products from 2009 – 2018, the review resulted in only one, Tanzania, establishing an export quota of 4,800 skins and 10,598 kg, including teeth from 1,200 animals and hunting trophies. The review did not result in recommended changes to management practices for Zambia, Zimbabwe, and South Africa. Mozambique and Cameroon were subject to trade suspensions that were lifted after submission of information and establishment of annual export quotas.
Given the unreliable nature of the unweighted trade data and the fact that the Reviews of Significant Trade also simply assumed that 12 teeth = 1 animal, it would appear difficult to have trust in these findings and the lack of any further action to restrict trade.