Smart Tiles make it very easy to get perfect measurements since you can cut it once they're installed. Just make sure you have a sharp blade and avoid using a sawing like motion. Back and forth movements are likely to dent the edge of the Mosaïk. Imperfections can easily be fixed by gently going over the edge again with your utility knife.
Should you have a small corner that seemingly wants to come off, there is an easy solution. A bit of "Pritt" like glue will do the trick. Simply put some of the glue on the rebellious corner, apply some pressure and off you go!