I know its hard to believe but the aftermarket units are worth it. You open so many options. I would never buy an OEM navi that is so out of date with the maps unless you only drive in your own city or county. On top of way more bluetooth abilities, you give yourself other storage options, better screen.
Weaknesses of stock navi units:
1) outdated maps
2) low quality screens (dated for 2007 technology)
3) extremely limited bluetooth and usb abilities (if you lucky to have a 2009+)
4) inability to watch movies or do anything while driving
5) Limited dual zone capabilities
Most people buy additional adapters and such to help but for the 200-400 you will spend for half these options, you might as well get it done right the first time. Its not for everyone but I definitely benefited since I wanted all these options.