It's not fully untethered, but after you get the Unc0ver app installed on the phone you can jailbreak again without a computer if the battery dies or you shut it down for whatever reason. And you can use something like ReProvision to make sure that the Unc0ver app stays signed on the device beyond the normal 7 days. I've been running it on my iPad and it's been very stable. Haven't had any issues at all.