Bean Bag friction mount holder for mobile devices

I'm in the market for a Bean Bag type dash holder for my mobile devices (cell phone, mp3 players). I want one that I can stash under the seat when I'm not using it, and I have a nav unit under my 2004 Prius drivers seat and JBL amp under the right seat so I'm not sure which ones would be small enough to fit under the seat.

Here are the ones I'm looking at:

The Bracketron UFM-200-BL model looks low height which is good for stowability and stability, the front of the bean bag looks like it could block the device (my cell phone has the antenna on the bottom so I'm a little worried about reception):

http://www.amazon.com/exec/obidos/tg/detail/-/B00178Y1IQ/ref=pd_luc_mri?_encoding=UTF8&m=ATVPDKIKX0DER&v=glance

The Arkon SM212 model is higher height, which should give better reception and visibility:

http://www.amazon.com/gp/product/B001DQQBVW

 

Anyone tried these or any other bean bag mounts for cell phones or mp3 players?

 

I saw the Bracketron in Best Buy and REI, and it seemed decent. The base is only about 6-7 inches in diameter, so it should fit on the Prius dash just fine. The only concern was that the pads are only on the forward part of the grippers, so that thin devices like an ipod touch will probably contact bare plastic, potentially causing scratching or poor hold. But I can easily add some more padding myself to remedy that.