I have not used the Santic shoes linked to, but from the look of the sole design I don't think I would like them. The problem is that it looks like they just took a road clipless shoe design and removed the cleats. But that is NOT what makes a good pedal for flats. Take a look at the sole of the Santic compared to a shoe designed for flat pedal use:

Santic


Northwave Clan:



Two issues I am seeing with the Santic:

1- The forefoot area (under the ball of the foot) is curved. If the sole is also stiff, this means it is not going to fully contact the petal from end to end, but rather rest more in the middle. Not great for traction or control. If the sole is stiff (which can be a good thing) It would have been better if they have flattened it out a bit.

2- The grippy area towards the front is wide enough under the ball of the foot, but it gets very narrow behind that, and does not extend back very far.

The problem I see with the Santic is that even when you pedal with "pedal forward" position (axle close to the ball of the foot) you are not getting good sole/pedal contact at the back of the pedal. And switching to a more "mid-foot" position (which is a great option you have with flats) really gives up grip and control. That area under the arch of the foot looks useless on a set of flat pedals.

All this to say that if you are going to go with flats, get shoes designed to work well with them. Heck, even some non-cycling specific shoes will work better.