Compared to GIC, compomers are inferior with respect to which characteristic:
Compomers are composites to which glass ionomer components have been added. 
Primarily light cured they have superb handling characteristics. 
Overall compomers physical properties are superior to GIC and RMGIC but inferior to composites.
They are capable of releasing fluoride but the release is not sustained at a constant rate and anti cariogenicity is questionable.

Reference-Phillips’ Science of Dental Materials / Kenneth J. Anusavice - 11th Ed Pg:328
Handling characteristics
Strength
Sustained fluoride release
Wear resistance