If Mondo were a major company like Amazon or Ticketmaster, they could spend limitless dollars on perfecting a checkout system. For a very small operation, they are doing the best they can. If they start charging $150 per poster, they will start pulling in enough money to pay for massive hardware and software upgrades--while pricing out the customers and reducing the demand that led to the upgrades in the first place. They are smart in teaming up with Sideshow to start releasing the variants through the SS site while they sell the less limited regular versions, and I can't wait to hear more about their partnership.
Mondo's site is working MUCH better than it did at this time last year, because they have been making as many improvements as they can with the available resources. I am surprised that such a small scale boutique operation has a site that works as well as it does, all things considered. They are practically operating out of a closet, yet they still strive to keep editions and prices low instead of selling out in order to make more money. They could go the Gentle Giant route and print 10,000 copies of everything and flood the market, but then the whole concept of limited collectible art would go right out the window.
It's unfortunate that you have to pretty much be a die hard glued to the computer screen to get an order in with Mondo, but there were days when it was like that with Sideshow at times. We melted a few servers back in the day! And people missed out, and people were frustrated, etc. That's how this hobby works when things are at their peak.