I would describe it as that for your opponent, it looks like vanished and in your place appeared a lock/some other item or person.
It is an old jutsu from the start of the series and not shown anymore in the anime and manga.
Maybe it should never have been used, because how it works and how powerful it is, can be quite confusing.
It isnt that powerful of a jutsu and not something frequently used in high lvl fights.
I like to believe that for a better than average shinobi (like high chunin, jounin or higher), it doenst look like you vanished but that they can see you make the swap with the item or person that you substitute with.
If it even looks like you vanished for a better than average shinobi, than the ability would just be to powerful.
It would almost be like spacetime jutsu and the subsitution jutsu isnt suppose to be that powerful.
It is a jutsu to create an opening and escape, with more of a prank level than seriousness imo.
These are my views on the jutsu.
I hope this answers your question.