I got one of Matt's black covers and have to say I'm impressed. All the things previously brought up by Matt and others I see, but again, the only glaring usage issue is access to the decomp valve and that is easily remedied on this early version as has been pointed out. Another option for a field fix is to superglue a plastic button to the top of the standard decomp valve. I don't have a 288 HD filter setup yet to test its fit but given Matt's attention to the rest of it, I don't expect any bad surprises.
I do a fair amount of shipping on eBay and feel I know a bit about it. Like Matt, I also would not feel comfortable shipping this in a bubble envelope, given the cost of it. And as a buyer, I would expect the seller to care about the item as much as I do.
Assuming USPS shipping, this would likely need to be shipped Priority due to its weight (10.9 oz) plus packing material and a box. I agree with others that Flat Rate would not be appropriate if you are trying to keep shipping costs down for a single item. A 12x6x5 box would be minimum but I think a 12x6x6 box is more standard. Using PayPal to create the shipping label, it would cost anywhere from $7.80 to $11.70, depending on where you are in the country relative to Matt. Plus figure another $1.50 for box cost, packing material, tape, label, and toner. If you use a Cash-Back credit card to buy the label, you can get a little money coming back (2%?).
So kudos to Matt for taking this project on! I look forward to its success and future offerings!