Re: Here's hoping...Android L inbound
The difference is this: the Razr M was built with hardware that predated the hardware designed to be used with KitKat. The Droid Turbo, as it is rumored, is using the same exact hardware chipset that the Nexus 6 is using.
I have a Maxx with KK and there are very few issues with KK. Battery life is not as good as it was on JB, but it is only marginally worse (maybe 1% per hour more drain in my experience.) But, again, the 2013 Droids (and the Moto X were built with a hardware chipset that was different from the Snapdragon used in the reference Nexus 5. There were some weird bugs with the initial 4.4 update, but the 2013 Droids were the only phones with 4.4 for a long, long time - the Nexus phones and the Moto X were the only other phones that had 4.4, were quickly update to at least 4.4.2, and all other phones that received KitKat were delivered 4.4.2 or later. Once the 2013 Droids received 4.4.4 (six months later...), all of the bugs that I know of - the double home bug; the Google account disconnect when the phone lost network connectivity; the bluetooth issues - were fixed. Except for the slightly worse battery life, 4.4.4 is working great on the Droid Maxx.
The Turbo will be fine on Lollipop. There may be some bugs with the initial 5.0, but hopefully Motorola learned enough last year to wait for the 5.0.1 release before delivering their first lollipop updates to their phones. If not, then the bugs will just be a little frustrating.
I will suggest this, though, if you get the phone: make sure you plan on a factory data reset after the update. It's a pain, but it always goes better. (I just had terrible bugs on my iPad after the 8.0 update and had to redo that from scratch, too. It's not just Android that works better with a refresh and rebuild after an update.)