The Hansajet, built by Hamburger Flugzeugbau, is quite a unique aircraft. It is the only one with a T-tail, two jet engines attached to the rear fuselage and forward swept wings through the fuselage. In addition it has tip tanks and curious cockpit windows, which are somewhat similar to those on the Beech 400.
Essentially there is only one version of the Hansajet. However, the German air force has used the aircraft as a trainer for electronic counter measures (ECM), for which these aircraft received a radar nose. These specific aircraft are known as HFB320ECM.
Confusion possible with
Apart from the T-tail the only matching characteristics between the HFB320 and MU-300/Beech 400 is the a-typical cockpit window style. For the rest they are totally different: low, backward swept wings, no tip tanks, larger oval cabin windows, etc.
As the only other bizjet with wings through the fuselage you might mistake the Hansajet for a Jet Commander. However the former has a T-tail, forward swept wings and more distinctive cockpit windows.
From a distance you might mistake a Learjet 25 for a Hansajet, because both have small diameter jet engines at the rear fuselage, tip tanks and a relatively small vertical stabiliser. However, the wings of the Learjet are nearly straight and attached below the fuselage. Moreover, the cockpit windows have a totally different style.