Both the TC and DM thermostats perform the function required in the Triumph/BSA triple engine application.

The TC design is more complicated so there is more to go wrong although having said that there must be thousands in use as transmission oil thermostats and probably several dozen in triple applications. In the triple engine applications there is only one failure to my knowledge and this is covered in Appendix I.

The DM thermostat is simple with little to go wrong and it has the additional feature of an integral rocker oil feed connection. In addition the oil connection sizes are better matched to the oil hose sizes installed on the triple engine.

The DM thermostat is somewhat more expensive than the TC Thermostat.

Having said that then on a personal basis I will be purchasing any future oil thermostat requirements I might have from David Madigan. In my personal view the extra cost is more than offset by:

a) Simple elegant design.
b) Built in rocker oil feed connection.
c) Better match of connection and hose sizes.
d) Supporting a guy who is dedicated to producing parts for the Triumph/BSA triple motorcycles.