The solo aid was designed prior to any spring loaded belay devices. Works like a clove hitch, though easier to feed when it gets tight as often happens without proper slack.
Thinking maybe the carabiner mod to the regular clovehitch system might be just as good?
The only way I got the Grigri to work well as an on lead solo device was with the cable support mod for chest harness.
But there are some experts out there who know more, hope they can post.