By your description I feel safe in saying you do not have metal stems.
Metal stems are "Bolted" in place against a flat rubber gasket on the wheel face. The following link will illustrate the range of metal stems available.
Chrome is not the defining feature of a metal stem. But rather the mechanical stability they provides.
I watched the Tire Minder video on their site. While I am not recommending their product the video does mention it does make a good case for the points one should consider when selecting a system.
The OFFICIAL WEBSITE of Minder Research, Inc. - Home of the TireMinder TPMS, TempMinder and NightMinder Systems.
And yes there is a considerable difference in the weight of the sensors in my system, purchased 4 years ago, and the newer systems. Mine weighed .7 oz. as apposed to .3 oz. that is now available