The MPPT design is based on the IC by TI, this is mostly to serve as either a nice generic unit for people to use, or as an open source reference design.
I'm no expert is designing these things, however I feel like the design is OK :)
The design is made to fit into one of the common aluminium enclosures available from China. These are often sold as 80x50x20 enclosures.
By using the XT30PW style connectors, we can allow for around 20A continuous current, and use an extremely common connector that is available worldwide.