This variant is very popular and extensively tested.
Some well known layouts or introduction to home row mods include Shift on + the home row, usually under the pinky. However, as we explained above, it is very hard to time + Shift properly on the home row when typing text at moderate or higher speeds, + and this generate a lot of typos. This is why we (strongly) argue against using a HRM Shift + to type text and (strongly) advocate for the sticky Shift instead. Consequently, the + default keymap do not include a HRM Shift.
+That being said, a Shift modifier on the home row can be usefull for shortcuts, especially + ones involving keys out of the primary layer (such as the Function keys). If you rely on these + kinds of shortcuts, you can activate the pinky HRM Shift in the settings. In that case, + make sure you don't start using them while typing text, as this habbit will come back to bite you later.
The reference implementation is called “Ækeynox”, and is available both for ZMK and QMK: