After market navigation system?

Anyone with experience in buying a non-factory navigation system? I am wondering if it is a good idea to add this to Z in that empty dash empty space.

Brother-in-law has a electronics shop in So Cal that specializes in aftermarket nav for all makes. He is looking at setting one up in my 05 G35 that came without nav. I'll repost if he gives me info on the Z.

I have heard many people doing this. But I rather just have it not connected to anything. There is a portable Nav system...I prefer that ^^