I have/use both, and each has their place in the shop, and each has it's own specific strengths and weaknesses.
A digitally controlled heat treat oven has the advantage of accurate, multi-segment heat treat operations, which is a requirement when heat treating most stainless steels.
These sort of operations are at best very tedious with salt tanks.
Salt tanks, particularly high temp ones, must be built with careful consideration in mind to achieve accuracy. If the actual tank is too large (too much volume) overshoot/undershoot becomes major issue. Generally the size of the salt tank should be ONLY large enough to fit the widest blade you ever intend to place in it.
The "salts" that are used in a high temp tank are generally a "neutral" type salt..... if, after a number uses, that "balance" of the salts depletes, it can literally suck the carbon out of blades. this is why salt tanks always have a layer of carbon/charcoal, etc. floating on their surfaces.... the salts "consume" the carbon from these materials to re-balance itself.
For me the biggest advantage to salts is the fact that I can take a blade very close to finished, and then heat treat it, and afterward only minimal clean up is required.... I particularly like salt tanks for carbon steels/ folder blades.
In the the end, both are essential pieces of equipment in my shop. There are many other differences, but those are just some that come immediately to my mind.
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