A "spindle guard" rigid and comprehensive enough to protect you from broken bits would probably get in the way or interfere with the material being cut. What's more usual are dust boots that surround the cutting area with flaps or brushes of some sort that can bend, so they don't bang into the workpiece when the tool descends or traverses a high spot, and still allow access to change tools. These will also help deflect broken bits as they fly out, hopefully reducing the risk somewhat. But you still need to wear your safety goggles anytime you're running your machine, and not just when you're looking directly at it.
But if you're really blasting your chips with high-pressure air, then an enclosure might be worth investing in; those sharp-edged chips will go everywhere without it. The vacuum will only pick up a certain percentage of them; you'll find another percent or two in your underwear...