Sounds like something may be a little off with the image you used.
Unfortunately there have been some images that didn't behave quite as well as they should have due to various builder issues and the like, but overall it's been pretty reliable for me. I've got two ALIX boxes running nano in production with customers and they're working OK, but it's just simple NAT+IPsec+PPTP on them. Worked fine and passed my tests before they went out into the wild.
I can understand being skittish about remote upgrades since nano is still being implemented, but it has worked for most people. Typically it doesn't leave a system unbootable, if the upgrade fails it shouldn't switch to the alternate slice, but depending on the date of your image it may not have all of the safety precautions.