Series 2001
Series 2001
According to Dave Kessler, whose shop was an authorized B&S dealer,
the Series 2001 and Medusa were pretty much the identical horns.
This is how he described them on the Kessler & Sons website:

The B&S Series 2001 is the predecessor to the Medusa.
For the tenor sax, the body tube is the identical design to the Medusa.
There are only a few minor differences in key design.
Here are the few differences we have been able to identify:

Series 2001: Low C/D# Cluster 2 Separate Rods. Medusa (Series 2006): 1 Split Rod Mechanism.
Series 2001: LH C#-B Rollers are 2 Separate Rollers. Medusa (Series 2006) 1 Roller; 1 Tilting Connector Roller.
Medusa
Medusa
According to Dave Kessler, whose shop was an authorized B&S dealer,
the 2001 Series and Medusa were pretty much the identical horns.
This is how he described them on the Kessler & Sons website:

The B&S Series 2001 is the predecessor to the Medusa.
For the tenor sax, the body tube is the identical design to the Medusa.
There are only a few minor differences in key design.
Here are the few differences we have been able to identify:

Series 2001: Low C/D# Cluster 2 Separate Rods. Medusa (Series 2006): 1 Split Rod Mechanism.
Series 2001: LH C#-B Rollers are 2 Separate Rollers. Medusa (Series 2006) 1 Roller; 1 Tilting Connector Roller.
Series 1000 (Intermediate)
Stencil Horns
Series 600 (Student)
Series 600 (Student)

These Taiwanese-made horns were introduced in 2002 and were the replacements for the 500 Series.

Both the 500 & the 600 Series were considered student model instruments.

Series 500 (Student)
Series 500 (Student)

This student model instrument was made in Taiwan.
It was introduced in 1998, and was to be the replacement for the Weltklang.
Production was ceased in 2002 when it was replaced by the 600 Series.