I use hardware cloth but not on the horizontal section. I leave that totally open and close off the vertical opening inside at the frame. Mine are probably framed up differently than yours.
Either one should work fine as long as they are installed firmly so a raccoon or such can’t just rip them out and the soffit vents are not a material the raccoon could just chew through. That would be my main concern, the materials the soffit vents are made from.
This thread is a little old but was hoping to get some advice on the soffit vents. Would like to know how well they work. I'm a little worried about pockets of air forming above them not allowing good airflow out the vents.