I'm not a LEO but I do teach DT and the feedback I get is that the gel or foam tends to harm the officers as much or more than the person being apprehended. Spray does a better job of staying where you put it but foams and gels splatter and spread. Of course, in close quarters, any OC tends to cause collateral damage.
Yep...Not to mention in the heat of the moment the number of officer that have pulled their OC spray and wound up blasting themselved full in the face..