Has anyone ever bought one? how much and are they as good or better than the stock navi that Acura has? woundering if its worth it.

 

There are many threads about this. The popular brands are Magellan, Garmin, and TomTom.

Please perform a search for details, but here are some threads to help get you started:
Awsome aftermarket NAV system
I need an aftermarket navi for my 04 TL

 

One issue you will have is fitment. I have a Pioneer AVIC-Z1 in my wife's Aviator. To be honest, it is a superior nav system to the factory TL. It can be configured for more features as the TL. It uses a database from a different company than the TL...and I think it's better. However...and this is a big "however"....the voice recognition isn't even in the same world as the TL. The TL is so much better. The Pioneer has a ton of commands you can use with VR...but it's no where near as intuitive as the TL and it doesn't work nearly as well. Pioneer failed to include decent noise cancelling software and that was a huge, huge error on their part. But we're hearing they are going to fix that. And with the Pioneer being hdd driven, software updates are a simple download away.

The Pioneer has NavTraffic...and for me, that's huge. Incredible oversight by Acura not to include that on all systems that have XM.

All in all...I would probably prefer the Pioneer unit to the Acura due to NavTraffic. But other than that, the VR capabilities of the TL make it a much more fun and easy system to use.