The problem is not the freeze plug itself, it's the overall situation.
You have an IMS tube that rotates axial, horizontal and vertical at very different frequencies and is accelerated and decelerated. Just think about that this thing is part of the valvetrain and every time the cam moves / hits a valve it vibrates a little bit. Also the IMS tube connects both valvetrains. One in the front and one in the back. So you have torsional forces within the IMS tube.
Next thing is that if the freeze plug starts moving, because the air in the IMS tube expands in worst case it will be pressed against the IMSB main bolt. The freeze plug rotates, the bolt is in a fixed position. Think about if you want that and what can happen to the bolt, screw and plug and in the end to the IMSB and IMS tube. Keep in mind that you have horizontal, vertical and axial forces and vibration. And you have vibration caused by combustion.
If you install the freeze plug like Casper Labs installed their "patented thing", the edge of the freeze plug can rub against the circlip that holds the IMSB in position. This might be a less bad situation as if the plug rubs against the center bolt at first sight. But if the circlip fails, everything will fail sooner or later.
As said before, the problem is to fix the freeze plug or anything else without harming the IMS tube (temperature, expansion levels, balancing, weight, maybe engine oil in the Ims tube to the bearing side) in a defined and fixed position.
That is why i said come up with a more sophisticated solution than a freeze plug.
And to be honest, i did like the freeze plug idea too at first sight, but after thinking of it in detail, i don't think that it is a clever solution. The clever solution would be if you can make 100% shure that the "plug" can't move in any direction, doesn't harm the tube and doesn't cause any balancing problems.
But if you insist on using a freeze plug… it's your car, your engine, your money.
Regards from Germany,
Markus