Taobao ships direct to the U.S. without a need to use an agent with a couple of caveats.
No quality control - Using an agent will grant you photos of the item to make sure it's what you actually ordered and leaves the opportunity to return though with an item as simple as an aluminium box, I'm sure you'll be fine.
Tax - I'm not up on U.S. import tax laws but you might have to pay customs a fee on goods entering the country. Most agents will help you... ahem... sidestep this issue by declaring goods at a lower value but this isn't full-proof. There are a million posts, guides and info on this to be had though the K39 is so cheap, I doubt fees will be very expensive.
Effort - Going direct means using Taobao, Alipay and Aliwangwang (a chat program and only way to talk to sellers). My account was suspended due to "suspicious activity" or some such (apparently this is quite common with foreign accounts) until I went on live chat and got them to call me to unblock my account. I also have to use an agent since I live in the U.K. so I use Basetao's "ship to me" service so I don't pay the usual service fees, just a modest extra on shipping.
All of my items are still sitting in Basetao's warehouse as I'm still waiting on a couple more items coming in and then I'll post most of it together to reduce shipping costs so I can't tell you what international postage is like but that's going to vary pretty widely depending on a few different factors such as: how quickly the seller dispatches the item. This is usually pretty quick if it's a common item but bear in mind it's fairly common for sellers to buy the item themselves only after you've bought it from them. This is common with more expensive or less popular items. It'll also depend on which shipping company you choose to ship with as well as if customs (both Chinese and U.S.) care about seizing, inspecting or otherwise interfering with your parcel. Some items may take just a few days, other may take weeks.
EDIT: My recommendation would be to shop direct with Taobao.
Install Aliwangwang (I installed it on a VM as I don't trust that it's not malware), and get good at translating chinese in google translate on the fly and make sure the seller understands exactly what you want before you order.
Only buy from sellers with plenty of feedback (go and look at how the Taobao feedback system works) one diamond is essential, five is better, crowns better still.
Use a credit card with 0% foreign transaction fees or prepared to be stung by your bank. Credit cards will also afford you an extra level of protection against fraud or non delivery of goods.
I've went and written an actual essay on how to use Taobao here, haha, hopefully you and some others can benefit from my experience though.