Larry, it looks like the developers are open to suggestions for new features, so you might wish to drop them a line. If it's a feature that would make your life substantially easier, you might want to think about how much it's worth to you and offer them that as a financial incentive. It's not like you can hire them to do custom work for you ($$$!!!), but something as little as $100 might get you to the top of the suggestion to do list. It all depends on the developer.
I think a big part of the price of a full service pos system is that it's been tested 6 ways to Sunday. It brings rock solid stability. You're dealing with a great deal of new technology here. The operating system, the software, the tablet, the wireless printing protocol- none of these have a terribly long track record. If you don't want to bother yourself with all the technological details, I fully understand, but I would try to have someone on your staff who might be willing to learn a bit about it in the event that troubleshooting might be necessary. There's a chance that everything will just work like it's supposed to, but with this much new technology (or technology in general), you never know. They don't have to be technology wizards- just to be able to understand the ins and outs of your system in order to minimize calls to pay support. Once you start spending a lot of time with pay support, any savings between this and and a full service system might evaporate.
You're a little off the beaten path here. You need a support system- and not just pay support. Whatever you, your staff, your family or friends can learn about this system, the better off you'll be. Sometimes it takes a village to keep technology running without spending a fortune
Android devices are a bit out of my comfort zone, but troubleshooting tech issues is my background, so if you need me, you've got my number.
Beyond making sure you have troubleshooting resources available to you, you might want to build a little redundancy into the system on the hardware side by having an extra tablet and possibly an extra router around as well and making sure both are configured. Thermal printers are old technology, but it wouldn't hurt to have an extra printer on hand either.
Lastly, I just took a look at the asus tablets and can't really tell if they force you into buying service contracts from ISPs. If they do, that $200 price tag isn't representative of the true price. Unless you want to use this tablet for emails and/or other online activities, you only need wifi for your needs, so you shouldn't need to pay hundreds of dollars a year to an ISP. Make sure there's no mandatory service contract with this tablet.