That is part of an ongoing discussion. Best I can tell the reason some have flys and others of the same design not is that the ones with flys are intended to be worn strictly as an undergarment but the no-fly version can be worn either way. I wear the 9 inch version as outer exercise gear and routinely go outdoors wearing them, tho I do not venture too far outdoors in them. Still if someone were to wear these as outer running gear that would be fine too. These come in various leg lengths in the same design with the longer 9 inch and even greater length versions seemingly more suitable as outer running wear. Your other option is a square-leg swimsuit like this
https://www.swimoutlet.com/p/sporti-...4/?color=10770
In the case of the Tesla shorts the black color will make the seams nearly invisible from a distance