I have a GE and put it on Shabbos mode every week. How does one know if it works well?
As far as I understand things, the sensors vs switches is just a technical interface issue, there might be a lot more things going on. Which is why I feel that from a שמירת שבת perspective one is safest with a device like Zman Technologies or the Supco device, which totally disconnect power to the refrigerator on a schedule, and let you know when power is on or off.
The highest level of chumrah in this sugya is to get Shabbos Keeper or ShabbatPro, or a refrigerator that has a shabbos mode that provides essentially the same functionality. Those address the following issue from your link:
f. "Mehadrin" requirements – Some people are very strict and will not open the door of a refrigerator while it is not working, fearing that to do so will cause the thermostat to turn the compressor on immediately....
As noted above, The Zomet Institute feels that it is not necessary to purchase such a special mechanism (which will typically have a relatively high maintenance cost).
Not every refrigerator labeled with a shabbos mode does the same thing.
If however you're not keeping that chumrah, and holding by this:
a. The vast majority of people accept the ruling by most rabbis that a refrigerator can be used without paying attention to the thermostat and without fear that opening and closing the door will cause the compressor to be turned on or to stay on for a longer time. Note that this approach has a firm halachic basis.
then it's fairly easy to see whether covering the door switches (or sensors with a magnet) is preventing the vast majority of the issues (lights, fans, etc.). If you're in that situation, the only other issue they point out is this:
However, in some models the computer receives its own independent information about the status of the door from another sensor, often a magnetic detector (which closes a switch when the door is opened) that is not visible from the outside (it is usually on the inside of the doorpost). In this case, jamming the switch on the door will not solve the problem!
Whether this is problematic at all is not agreed upon either. For example, I can't imagine the Star-K holds of this as a problem in and of itself, considering their shitos regarding oven temp change on yom tov.