Why would I use a displacement insert?
FAQ from Radleys
Displacement inserts are often recommended for use with open bath Huber models (e.g. Ministats), when they are connected to a jacketed lab reactor (such as Reactor-Ready) as opposed to when placing items in the bath.
With open baths, whenever you need to change the temperature of the oil in the vessel jacket, the temperature of all the oil in the bath needs to be changed too, which takes time. Because the baths are open to atmosphere (exposed to oxygen and water vapour), the oil can degrade quickly. There is also a risk of the oil overflowing, if it is heated up a lot and expands.
A displacement insert takes up some of the volume of the bath (an empty container in place of oil), reducing the three potential issues described above.
Note that Huber Unistats have a different, more advanced design than bath units - Unistats are hydraulically sealed, with a smaller internal volume. Displacement inserts are not applicable.