The detailed design of the two thermostats are different but both are based on the same principle of using a commercially available wax capsule.
The use of such a wax capsule is very sensible as these units are manufactured in vast quantities for use in vehicle water cooling systems and are extremely reliable over extended time scales.
The DM design is simpler and more elegant than the TC design with fewer parts. It is also much easier to assemble.
The DM design also incorporates a connection for the rocker oil feed. This could be blanked off if it were wished to retain the standard rocker oil feed.
In the tests carried out both units performed well and did the job required satisfactorily.
Neither unit completely isolated the cooler oil flow in the "cold" condition.
This is not a disadvantage in my view as it gives a very small oil flow through the cooler when cold. This is the situation for most triples for most of their operating life so the small flow through the cooler even with the thermostat "closed" ensures mixing of the oil and aids complete filling of the system from a "dry" starting point.
Equally neither thermostat completely 100% closes off the by-pass route for the oil when the oil is hot and the thermostat open. This is because neither thermostat has 100% sealing of the valve. However the tests show that even though the sealing is not 100% it is very close to it and certainly sufficiently close for all practical purposes.
One difference between the two thermostats is in the labeling of the thermostats of the different connections.
Although the TC Thermostat is labeled for a transmission cooler the engraved labeling is quite explicit and connecting the pipes correctly is straight forward.
The DM thermostat does not have the connections labeled. It would in fact be possible for the unit to be connected incorrectly and for there to be no flow through the thermostat.
This could be overcome by clearly defining the correct connections on an installation instruction sheet. However bearing in mind that these instruction sheets are often only read AFTER the unit does not work and are normally not available to the second and following owners of the unit it is recommended that the correct connections are engraved or etched onto the DM thermostat. As the DM logo is already etched on the unit then presumably it would be possible to do this.
With this one caveat, both the TC and DM thermostats work as intended and the DM unit has the additional feature of the rocker oil feed connection.