Keep in mind it is no different than this.
If you look at the PDF for the Evo I attached look at the diagram on page 11 item 6.
The electronic controller on the BRS is not submerged but hung on the wall.
The EVO is attached to the outside of the unit not on the wall.
The probe is on a cable and the BRS is free air so to speak to be placed in the tank or sump.
The EVO is on a cable but put into a bulkhead fitting in the flow tube.
The heater unit on the BRS unit is submerged and is placed inside the tank and the water is in contact with the exterior.
The EVO has the heater coil wrapped around a tube and the flow goes through the tube.
Either way they both just have a titanium skin separating the coil from the water.
If the barrier fails the result is the same.
There is just a sheet of titanium isolating the coil from the water on both them.
Its all the same parts just assembled differently.
None the less the same potential for water to come in contact with the heating element.
Additional but minor concerns I had,
were small leaks and or salt creep at the probe and flow switch locations.
Flow switch is a safety feature so the unit will not operate if the flow shuts down so it will not meltdown.
Now if we are talking about the Cobalt's or Eheim heaters then yes you are 100% correct.
You might as well just drop the end of an extension cord in the tank and watch the fun begin.
But we have to do an apples to apples comparison here.
Now that I have revisited the thought on inline heaters I have come to the conclusion that there's potentially more failure points and potential faults than the separate parts.
What is the heat loss to the exterior of the heating tube?
I am positive there is some insulation but heat will radiate out for some loss.
So would I need a larger heater to do the same job?
Then all the fittings that have to be assembled that are in contact with the water. Unions and gaskets, probe port seals, all will leak eventually and need to be cleaned and replaced.
Anyway in the end its a choice and all pros and cons need to be evaluated.
I do not feel one can go wrong with either solution to be honest.