Quick update:
Performed to short (2 mile) journeys today and didn't have any lag. I am reporting the problems I find to Sygic.

What I do like about it is that once you get used to the screens it is quick and easy to use. If I have a few more trouble free journeys then I would conclude that the lag may be a gps issue as the previous poster has mentioned.

I will post back with further info as acquired.