I think the clip looks great. The thick spine threw me off a little since the computer graphic showed a thinner one, but it makes sense to need that thicker spine, especially since it's glue holding the piece together. Without it, the clip would look flimsy.
I think it would look good with vertical stripes - they're very slimming!
But I'm betting that the horizontal stripes function better and make the sides stronger and more durable. Sure, one wants it to look good, but if it doesn't work well and last long, looks don't add up to much.
Consider making different spine widths. Some decks are thicker, some thinner, depending on the precise stock used. You won't be able to make this into a "one size fits all" thing.
Did you ever see De'vo's wooden clip? It was actually enclosed not at the spine, but at the top and bottom - it's like a box with the long sides left open. Something similar might make a nice alternative design down the road when you get these things selling far and wide. If you opened the short top and bottom sides instead, it would function as near-impervious protection against deck damage!
