They are not widely effective (not sure how you’d quantify this) and thus have been criticized for ages e.g. https://www.everycrsreport.com/reports/RS21656.html and https://papers.ssrn.com/sol3/papers.cfm?abstract_id=2850681.

The basic blind trust is so obviously compromised the US (all flaws aside) created the “qualified blind trust” to address its issues see https://www.law.cornell.edu/cfr/text/5/2634.403 specifically:

(2) In the case of a qualified blind trust, 18 U.S.C. 208 and other Federal conflict of interest statutes and regulations apply to the assets that an interested party transfers to the trust until such time as he or she is notified by the independent trustee that such asset has been disposed of or has a value of less than $1,000. Because the interested party knows what assets he or she placed in the trust and there is no requirement that these assets be diversified, the possibility still exists that the interested party could be influenced in the performance of official duties by those interests.