How long is the pre-order window? I didn't see that on the site, but might have missed it.

Until the Kickstarter starts, which is planned for November. At which point you can redeem the coupon and back the Kickstarter and get it at a “special price” which is estimated to be $379 (might change up or down). Presumably this is lower than the Kickstarter price itself without the reservation coupon. A bit of a convoluted system, but you can get your $20 back anytime, and it automatically refunds if you don’t back the Kickstarter or the Kickstarter never launches, so that’s cool.