The mechs they are piloting at the beginning of the episode are not prototypes! These are the main type of mechs piloted by the Federacy called the Vanagandr (whereas the mechs the Republic gave the Eighty-Six were called Juggernauts). The Vanagandr focus on having lots of extremely durable armor which makes them super heavy and slow. They also require 2 people to operate - one driver and one gunner. The Juggernauts were smaller, faster, had higher mobility but the armor on them was crap.
A lot of the military terminology is based on things from WWII, hence the heavy amount of German.
The new mechs after the title card are the new prototypes, the Reginleifs! They are modelled after the Juggernaut with better firepower, customizability, armor, and just overall better tech while keeping the high speed and mobility. Shin has his modelled exactly like his old Juggernaut, with the high frequency blades replacing the secondary machine guns.
Interesting fact about Eugene's death: in the anime, his impending death is pretty obvious. This is due to the fact that the anime tells the events in chronological order. In the light novel, you learn of Eugene's death FIRST, then it goes back and shows all the interactions between Shin and Eugene.