So far I've only been using my iphone... I have an old iphone that I can leave in the car.

The early version of Palmer's Dash Command was really poor, but has vastly improved.

The thing I like abou the kiwi is it's compatible with laptops, and wide array of software, where the griffin is probably going to be Proprietary products only.

As far as accuracy, everything seems spot on.

If you enjoy playing gadgets I'd definitely recommend it. But I'm sure the laptop software for the kiwi is much better for tuning.

As far as iphone vs android.

iphone usability is far far far superior to any of the android UI's...

Of course being open you can install better GUIs, but I just want my phone to work.

As soon as iphone is available for other networks, I'll be switching, but for now:
iphone AT&T > (any android on any network)