After browsing around our foot gear for awhile you'll probably notice we have a whole bunch of regular sparring shoes and then a whole bunch of shin-instep guards. If you're not sure which one to choose, read on.
Classic foot pads are great for covering the foot (as you might suspect). However, that doesn't do you any good if you get shin-to-shin contact during a match. Therefore a lot of practitioners opt to wear shin guards as well. Unfortunately, when you have them both as separate entities, they can be prone to shifting and twisting on you which can leave you unprotected when it counts.
The shin-instep guard was designed to reduce those incidences of equipment failure. Most are designed with either elastic straps around the shin and bottom of the foot, or a neoprene sleeve that slips around your thigh securely. The combination of the two elements help keep the whole thing in front of the most vulnerable parts of your leg.
The one real weakness of the shin-instep guard is how open it leaves parts of your foot. Just on visual inspection you'll notice that the traditional foot guard is able to cover the entire top of the foot as well as the sides. The instep guard leaves the toes and ridges of the foot open, making them more susceptible to damage while fighting.
It can be difficult to combine the benefits of both styles. Ultimately your budget and the quantity you need are going to help point you in one direction or the other, not to mention any special needs you might have due to prior injuries.