With the Avent bottle warmer, both liquid food and baby food in storage cups, jars, cans and in bottles from Avent and other manufacturers can be heated without any problems. As long as there is enough water in the device, the glass should withstand the heating temperature.

Yes, we warm baby food from the jar with the bottle warmer every day, but we always transfer the contents from the jar into an Avent plastic cup (see Digitec item no.: 451121). I wouldn't put the glass directly into the bottle warmer => it could get too hot and break.
We warm the porridge in the cup on the medium (porridge) setting.