Is the GSS mulligan a thing?

For reference, from Magic Wiki: Gabriel Special Surprise, or GSS Mull - Where each player initially draws 10 cards, then selects 3 cards that they do not want and shuffles them back into their library. I saw it, tried it and liked it, but it somehow feels weird / too easy / too convenient. We still use it in our playgroup, it's slightly faster than other mulligans and helps getting the lands.

Do you even know that stuff and how do you feel about it?