Billy.... I dont use mppt, and never will.
Not because I don't think it is useful, .. it is useful, but only if you build a miss matched ( poorly thought out) system.
I can't use a mppt in my system, as it would not help it at all... not even a little bit.
If you choose you cell size properly ( ie 6x6 not 5x5 ) for the same size panel you will end up with greater gains than a mppt is capable of. So a 5x5 72/144 cell panel will be way over voltage for A 24V system @ 5.5a or thereabouts.... you need mppt big time.
But if you buy 6x6 cells, you will have 8.8amps before you do anythin, and only a small differential to overcome.... which is too small for the buck to be useful for.
So the wrong panel selection costs you over 30% losses which you then try to make up with mppt.... not for me.
Secondly , a buck failure in the mppt may cause savage over charging, as your start voltage is way over the top, where in the 6x6 cell units, they will drive a bank up to just over comfortable equalise charge.
So no hope of me playing with them.... but they are simple enough, use a nano and buck.
..........oztules