It is true that you can fit an alembic or column extension to a Grainfather.
However, this does not make the Grainfather a great distiller. The alembic top makes it a simple pot still. While you can distill spirits with that, it takes several runs to obtain a significant amount of distillation. The T500 column is a step up from the alembic top, but not a great one. The column will provide more reflux, but it is small diameter and too short for a lot of jobs. And the Grainfather has limited mash heating power. But it will distill a mash nonetheless.
People tell me it is quite easy to convert a boil kettle to a still by soldering or welding a TC fitting to the lid, adding a method to clamp the lid down as well as a gasket and adding a modular column made of triclamp spools.
It's two completely different distiller kinds we are talking about.
The alembic, or pot still, of which an example is the copper alembic sold for the Grainfather, is a product to obtain the "normal" amount of distillation, i.e. you dont' strip all flavours (head fractions and tail fractions): if you want to make with whisky, rum, grappa, tequila, or any fruit brandy, normally you would either make a "one run" distillation with an alembic, or a "double run".
The column still is the instrument one uses to obtain a "neutral", an alcohol product which as very little congeners and which is mostly ethanol. This has, in a sense, "no flavour" and is like a blank slate which you use to make liqueurs, bitters, amari etc.
So if your goal is to make whisky (which is the normal first attempt for a homebrewer, I am actually making neutral first) a pot still is the usual, traditional, "kosher" way to make it. If you want to make a fruit brandy (grappa, palinka/slivovitz, marillenbrandt, etc.) then, again, the normal and traditional instrument you would use is an alembic (a pot still).
If your goal is to make an Amaro, or a Bitter, or a Mistra/Ouzo, then you must obtain a neutral first, which is really neutral, and then you add herbs according to various tecniques. The column distiller is way more practical, or safer, for that kind of distillation. The T500 column can be applied to the Grainfather to transform it into a column distiller.
Both column and pot still have their place in the distilling realm. They are different horses for different courses.
You are not bound to buy the T500 column if you have a Grainfather. You can adopt a column of your choice to a kettle cover of your choice. But, importantly, the kettle must have the possibility to "lock" the cover in place. This is something that the Grainfather has and my AIO doesn't have.
Not every kettle can be transformed into a still, only a kettle which has a lock mechanism on the cover.
For my distilling needs, I have a normal beer-kettle which is modified by the producer on my request to serve as a still (reinforcement bars on the top, safety valve, and a hole for the column/alembic). On top of this I have a "modular" still, I can use it in alembic configuration or in column configuration.
I cannot do that with my AIO homebrewing kettle. Modifying my kettle would cost too much and would bring too little rigidity for the heavy column I have.
With a Grainfather, you have an easy access to both realm of distillation (pot still and column still) in a simple way. Don't throw it away just because the heater is broken, that's a cheap and replaceable part. And for distilling you don't even need a controller, actually. Just repair the heater and you can use an external voltage regulator.