It's a good phone that could be great (not as great as the MAXX 'cause of that battery life and no wireless charging) - I would say don't hold your breath for an unlock for the bootloader or even root nowadays, it's getting way too tough to root and bootloaders are pretty much... well, locked up I suppose. I don't know of any devs that are seriously working on the Droid devices anymore, it's kind of a crapshoot if you find one I guess.
IF I had gotten either of them before that "Chinese guy" stopped providing the bootloader unlock codes I may have developed a different opinion, but I missed that window of opportunity and so I decided holding onto those phones wasn't feasible given my requirements.
As I said in another post, I did like the MAXX and Mini when I owned them recently, but the fact that I wanted a bit more capability meaning root access because I use some apps that require it as well as the option of potentially using some customized ROM or doing customization that might require something like the Xposed framework means you're dead in the water with the Ultra/MAXX/Mini.
I sold both, picked up a Samsung Galaxy Express for $80 and it's unlocked (for T-Mobile, did that in 2 minutes), rooted and of course running CyanogenMod 11 aka Android 4.4.2 without a single issue so far except the camera FCs often but that's a well known bug that persists and likely will always be problematic (except on those new CyanogenMod phones I suppose since they're designed to run that OS 100% without problems).
The Ultra, the MAXX, and the Mini are damned nice devices if you like "pure stock" and pretty much zero chance of them ever being anything else - the fact that they're GSM unlocked from the factory is a plus, so is the wireless charging for the MAXX and Mini, but that's about it for me and not enough to keep them for the long haul.