False. The Pfizer and Moderna mRNA vaccines both ceased to be "experimental" when they reached their respective Phase 3 trial endpoints, proving safety and efficacy.
See also: Pfizer Trial Information
MRNA vaccines have been in clinical trials for cancer and at least 9 infectious disease trials since 2013. The ingredients have all been extensively tested for safety.
Samples of prior studies:
Preclinical and Clinical Demonstration of Immunogenicity by mRNA Vaccines against H10N8 and H7N9 Influenza Viruses