I guess I'm a dunce, but I can't figure why I'd hold a deck lengthwise to shuffle, when it's so much easier to hold the cards crosswise? Or is it about that snazzy card shark move, riffle and bridge, in the video link? Never seen that method before today!
I feel it's kindest to the cards to overhand shuffle; that way you can move backward and forward among the cards in the receiving hand, randomizing the order, using new slots, and though it's slower, I'm taking time to focus on the question anyhow. The riffle and bridge method looks almost mathematically predictable in how the cards are going to be rearranged: divide by two, alternate left and right, divide by two again, alternate left and right again. The more skilled the shuffler, the more predictable the shuffle using that method, I'd say.