The 505 is a proven, solid device that gets very good reviews from its owners. But it is the last generation in terms of technology.
The pp has more features than the 505. But it is unproven at this time.
So, if you want a device that just works then go for the 505. If you want the latest features go for the PP.
I'm not trying to be silly here because given that statement the obvious choice would be the 505. However, I choose the PP. Given the nature of the device and this forum I suspect that we have many people who prefer to be at the leading edge -- even if it hurts a bit
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