You have the iGO 90500, which has also TTS ;), Plus TMC (like Primo) Plus Outlook contacts import (unlike Primo)
Main difference between iGO and Primo is the looks. Next Primo has some nice features, like truck routes, smart routes, green routes (less CO2 theoretical), better looking junction view, possibility of using new Nuance TTS voices (Loquendo TTS voices work on iGO and on Primo), ...
Also Primo has some extras like screen shot, reconversion tables (liters-gallon, miles-meters, Euros-Pounds, ..), foto viewer, some others I can not remember now.
Most of this is possible on iGO too, using a skin (for truck routes a special iGO build). Junction view is implemented in iGO, but in Primo it is real eye candy.
On the negative side, Primo is said to calculate some odd routes and crash in tunnels.
Both calculate routes and bring you there. Which is the main purpose, right?
In short, Primo is the navigation program I would let my wife use. No offense ;)
But for me, Primo is not my choice, iGO is.