This exactly.
FWIW, LAB CEO Sam Hahn also advises to err long in a broom/sweeper, as cutting of 1-2" is easier than extending.
If you really find yourself gripping down all the time due to comfort, you can still cut it anytime.
When figuring out length for my custom LAB, I chocked down on a 45" Taylormade broom for multiple rounds and it works just fine, if you dont insist on having your thumb on top.
Speaking of thumbs: Its VERY personal. Just try a bunch of different ways to grip the right and the left hand and find what makes the stroke the easiest to repeat. But be careful: The "right" grip might not feel natural right away. The lower hand grip I use now (suppinated right arm, palm "under" the grip and upper arm sticking to the upper body) felt super weird at first, but it makes the stroke absolutely automatic. Took me 5-7 rounds and multiple practice session to make it feel somewhat "normal" but its still a little weird.