The Pros And Cons Of Internal Heater

Brief introduction of internal heater: The wort heater mounted vertically in the kettle. The heater is tubular heater. When the wort is bloiling, the wort heated go through the tubular heater from down to up. And install umbrella covers above the heater. It will make the rising wort to surround and avoid the bubble formation. The wort will heat evenly.

1.Pros:
Less investment,no maintance and no fray.
Low power consumption.
Small heating radiation loss.
Boiling temperature and evaporation rate is adjustable.
Can be heated by low-pressure saturated steam.
The wort has slow flow speed in the heater bundle.
Simple device,no need external heater and stirrer.

2.Cons:
Difficult to clean. It will need to complete clean after producing a certain batch and will delay production.
Due to the wort with slow flow speed, the steam temperatue will be overhigh if won’t well control the steam pressure and turns out the wort partically overheating. It will result the colour deepened、bad taste, also will influence the quality of beer.

I think you're referring to a Calandria. I don't think the comparison is as clear as it should be, possibly due to the translation.

An internal Calandria simply increases the heating surface area inside the kettle. The surface area is designed into heated tubes, which convect the wort from bottom to top. Sometimes a pump is used to start the convection and aid in agitation during the  boil.

There is most certainly boiling and bubbles, which can be seen in this short video:
https://www.youtube.com/watch?v=ciJZGq-Bqaw

I don't agree with the darkening of wort, when using low power (15 psi) steam. This steam is only about 250oF which isn't high enough to cause significant darkening of wort, no matter how long it's boiled. I have a hard time believing that picture, because I haven't seen anything like that from Calandrias or even direct fired systems with extended boil times (up to 4 hours).

External Calandrias are another thing. They work by pump, creating pressure as the wort runs through the heat exchanger, causing large amounts of steam to come out the other end. They are effectively using the kettle as a reservoir, so one doesn't see a traditional boil.