Eventually I would like to compile all this info into a buyers guide. But for now I will just post some things as I think of them.

Light Source:
Wejex-incandecent small bulb running off of about 5 - 10 VAC
EG&G-xenon flash tube

Exposure Duration:
Wejex-one second, controlled by a shutter driven by a clockwork motor.
EG&G-1/100, 1/1000, 1/10000, controlled by fixed capacitor size and fixed resistors.

Wejex-sturdy metal, but spring loaded so need 3 hands to load film. Opens TOWARD the operator.
EG&G-flimsy plastic, connected to trigger so chance of premature firing. Opens AWAY from the operator. Stays open for loading.

Place to put filters:

Method of adjusting exposure:
Wejex-variable resistor for light intensity
EG&G-3 choices of exposure duration. Intensity must be controled with ND filters

Power supply:
Wejex-simple transformer, runs from alternating current.
EG&G-complex 700volt filtered and regulated AC power supply with a rectifier circut. Unfiltered DC output (no filter capacitors to replace or to blow up)

Mfg. Specifics:
Wejex-now made by Tobias; still in buisness, though support for the older white light models may be NA.
EG&G- still in buisness(?), though support for the, no longer made sensitometer may be NA.

Shop manual or owners manual on the internet:

Light chamber:
Wejex- built in
EG&G- removable

What I like best:
Wejex- I like the fact that it is so simple. It can be copied or rebuilt from simple components (older white light model). Newer models may be more complicated.

EG&G- Excellent workmanship and circuit layout. More complex than the Wejex, but still primitive enough to be fun to work on.

What I don't like:
Wejex- little light bulb may be too yellow even with 80A filter in place. Color temp probably changes with lamp voltage. Though, these factors probably don't matter much in real life film testing for gamma.

EG&G- some components are specific to this unit and are probably unobtainable (like the monster super-fast discharge capacitor). Suitable replacements ARE available, but may alter the function of the unit. Though, who really needs exposures of 1/10,000 sec in fine art photography. Those fast speeds were for matching film sensitivity data to high-speed xenon flash subject matter.