They are better. more flow etc.
the eheim core design is the same, so the amount of media you can put in there is also relatively the same, except in the heater models where you have to leave the bottom free, and in the other ones like the 2028, you can put something in the last layer (under the last basket). I use that space for nitra zorb or something like that...
I have both the fluval 405, and the 2028 and have tested dozens and dozens of other filters (eheim and fluval), and the ones I have are the ones I would keep purchasing in the future.
also, with the thermo filters, you need to adjust the thermostat on the heater and read the temp on the tank. meaning there is no 28 degree setting for example. you turn the knob, wait for a few hours and then tweak the temp as needed.
only the 2326+ come with digital temp controllers, but by the time you shed out that sort of money you are better off buying a 2028 and a 2215 or something like that.