I don't think any kind of warrior ever wore metal shoes, not even knights. So yeah I don't think he would be so eager to step on spikes. But that was beyond the point anyway.
The soles of knights boots were hardened leather, so you'd need metal caltrops to pierce them (but depending on the soil the caltrop might also dig more into the ground not doing much)
Also, caltrops take up a lot of space. So unless you were carrying a large bag of them, their effectiveness are limited to spiking roads.