This class is actually "just wrong". It uses the term "full caster", but it doesn't actually work with the Bard class which is a full caster. It should be explicit that only Druid, Cleric, Wizard and Sorceror can work with this class.

The wording is rough at several points, especially the Mystic Tradition ability which clearly confuses "and" with "or". "HP at higher level" is wrong.

From a balance perspective, this class is pretty powerful. It gets access to all of its spells "on time". It gets to cast Wizard spells in Medium armor. It also gets most of the class abilities at most a level late. In fact, as designed, it gets all of the class abilities at some point. Its only limitation is a kind of awkward limit to the number of memorized spells.

Overall I'm really neutral on this. It's not really polished, it makes very different trade-offs from previous versions of Mystic Theurge and I think it's a little too powerful.

I would not let a PC run this in my campaign.