#1
I wondering what is the difference between Chris Boderick's Pick Clip and a thumb pick. They both look like the same thing.
#2
The thumb pick is a pick that wraps around your thumb. The Pick Clip is a metal thing that goes on your thumb to hold a pick of users preference. Basically put, a Pick Clip is a customizable thumb pick.

In my opinion, the pick clip is more suited towards metal/shreddy stuff, being developed for the purpose of 8-finger tapping, retaining pinch harmonics, and using a pick shape that you like and a standard thumb pick is better in applications for any kind of finger picking type style. Just to restate, this is just how I see it, and I'm sure people use the picks in the opposite way of how I see it.

Hope this cleared the confusion up for you.
Ibanez
Universe UV777 Signed by Steve Vai
Prestige RG2027X with Bare Knuckle Aftermaths
RG7621 swirled
Prestige RG1420
AEL207E
#3
The pick clip is for holding a pick when you aren’t picking. A thumb pick is for picking with your thumb and having it sound as loud as strings plucked with fingers.