this is all about consistency from dead ball to delay of game and having one less thing for the referee/crew to worry about between plays. Subvarsity games have much more lax enforcement of the play clock with or without visible clocks so it doesn't really matter which system you use if you even closely monitor it. Where it's still really nice there if you use the 40 is end of half situations. A team will know exactly when the play clock would expire if they are trying to consume time. And the defense will know you aren't cheating them by delaying the start of the 25 second clock and using extra time.
Consistency always has, and most likely always
WILL REMAIN firmly in the grip of the R (for that specific game being played). Specific to the NFHS environment,
"Stuff" is likely to continue happening that may occasionally impact "consistency", and it will be up to the R to deal with unexpected (or inconsistent) "Stuff, as best suits the circumstances in which that "stuff" is happening. Access to that flexibility is critical. The play clock still starts when the R starts it, and it ends when it, or the half, expires.
As our NFHS Game Officials Manual suggests,
"In addition to a complete mastery of the rules, game officials must have a good knowledge of human nature and the ability to control situations as they arise.... At times, the emotions of players, coaches and crowds run high and game officials must control themselves in order to provide necessary leadership......Game officials must havea football sense which supersedes the technical application of the rules so that the game goes smoothly. Game officials are expected to exercise good judgement in applying the rules." At times, rational flexibility tailored to address abnormal circumstances, provided by relevant judgment, serves better than arbitrary compliance with rigid requirements, when
temporary circumstances deviate from normal, or expected.