Does anyone have experience with the Navigon iPhone app and how it compares to a standalone unit? I found a decent looking refurbished TomTom unit on Amazon for about the same price as the Navigon App, which I had intended to buy. But this morning I went on Engadget and saw that Navigon had updated its app to include text-to-speech for street names, which is THE killer feature for me, so now I'm torn. If anyone has any opinions on this, I'd appreciate them. Thanks!