After a while using mine to do some charging and an experiment with parallel rather than series (why I wanted a buck to start with), a buck (and by extension, MPPT) is of little point with less power unless your target voltages are WAY below the panel's output.
Even then, if the panel is small enough, the losses in the buck will negate the gains. I'm keeping mine around as a now optional addition because there are rare occasions when I need to charge a 6V lead acid from the panels. But for 12V, I've set it aside; I get a tad more juice by just running the panels in parallel.
If the runs are really long, and the wire small enough, it might be practical at 12V. But for me, using 100ft of #14, it's practically a wash, with winning tendencies in the direct connection department.
Shrug. It was a lot of money to throw at something that isn't in the loop anymore, but I have a suspicion it will mysteriously reappear at a later date when I upgrade the panels. When the current starts piling up in the lead-in, the buck will reveal it's glitter.
I'm thinking some additional mods to mine and 48V nominal panels will make for a sweet combo.
Steve