Well I took the plunge and tried out this controller over the last 3 months. In its original form I was not not happy, since the voltage fluctuated over too wide a range in my view (while in "float" mode for example). It would not keep the float voltage close to what my batteries should have, often wandering up close to 14V. Additionally, every hour or so in the afternoon it would rise up over 15V and trigger my inverter's over-voltage alarm.
Turns out that, beside continuous small adjustments of the MPP for tracking, it periodically re-does a full "sweep" of possible max-power points to make sure it's still running at the overall optimum. But, during that sweep, which takes about 20 seconds, it had no limit on the charge current and battery voltage, and when my batteries are full that was enough to bring them over 15V. This is a 12V 450AH battery system and 360W PV.
After some discussion with the makers of this device, they kindly made me a modified version of the firmware chip, and it's been quite fine since. It runs fairly cool, but warms up enough to affect the temperature compensation as the sensor is internal, I wish it was external to keep it closer to the battery temperature.
Note that this was a fairly new design so the firmware is still evolving. I don't know if the changes I suggested have become standard in their production, but if not then perhaps one could ask them for the same firmware as they made for that pesky guy in Vermont.
The change they made for me included:
* Narrow the voltage range (in float and absorption modes) to 0.25V. That's about 2%, and the hardware is apparently not able to make the range any narrower than that, but that's 3 times narrower than it used to be.
* Make the "low float" setting 13.25-13.5V. (In the 12V mode, nominal voltage before temperature compensation.) This is lower than what was available before, and closer to what Rolls/Surrette recommend for their batteries.
* Make the "high float" setting 13.5-13.75V. (In 24V mode these are doubled.)
* MPP sweep is disabled if in float (or absorption, which is just a higher-voltage float). It is done during bulk mode, and in float if the loads bring the voltage down lower than the float range - it essentially returns to bulk mode under such condition.
* More "night time" before switching the AH logger to the "next day".