I have a Mitsu 3 zone system that has 2 mini split wall units controlled by individual handheld IR controllers and a ducted zone that is controlled with a wired PAR-31 MAA Controller. I tried the MHK1 on this zone with no luck. I ended up selling it on Ebay. MHK1 does NOT work on IR.
The Remotec is a “dumb” IR controller. It will send out the equivalent IR signals that the handheld (HH) controller does. It does not control through the HH so if the HH turns the wall unit off and the Remotec then turns it on or changes the temp, the HH still thinks the unit is off. You can use the HH to override the other by cycling through some commands.
I have found that the Remotec will give you the current mode, temp and set temperature if you send a refresh command.
I also thought the SmartSence Sensor was discontinued because it is not on Amazon but it is offered on the SmartThings website today.