I have experimented with click track measure(s) and the count-in only metronome, and I tend to favor the first way, where I add a 2nd midi track to my drums track folder and just have that click track loaded with hi-hat ticks on the beats.
I found that often, when trying the count-in only for the metronome, (whether or not metronome is on/off during recording), and having NO blank measures ahead of the song's actual start, that MANY musicians - myself included, would have some initial audio chopped off, if anybody came in at ALL ahead of beat 1. Even just a very few midi ticks ahead of beat 1 would mean that the first note(s) on my keyboard tracks would not sound on playback, simply because the Note On event did not get recorded if it came at all ahead of the actual beat 1.
So, once midi notes get skipped over enough times, EITHER the keyboard player would themselves start coming in a fraction LATE, because they became gun shy about playing even a minute fraction prior to 1, OR edits would be needed to alter the actual starting Note event data to begin truly at 1, etc....
Either way - I just went back to including a measure or so ahead of the first 'real' measure of the song, and had a midi track with hi-hat or whatever and I have just been doing it this way for a long long time now.
Bob Bone