Personally I think it is a bit of a waste.
True tomato & potato are of the same family but the end result we want is different.
That is; with the tomato it is the fruit we require and subsequently the seed whereas with the potato we want the tuber not the fruit, the fruit is poisonous.
A high potash feed e.g. tomato feed is to ripen the fruit whereas the tuber we want from the potato is basically a root formation and is more likely to need a phosphate feed if any.
As I say I think it is a waste of time and in my opinion if a good general fertiliser is applied at planting out time this should be sufficient to produce a good crop of tubers!