I only look at the go-pro and yep, I hit the shifts EXACTLY where the light comes on, Always trust my gut and seat of the pants.

The only time I will look at the tach is if I want more RPM for the 2 step on the launch and also what I'm pulling as I cross the stripe.

I'm about to put a playback tach in my car b/c I can't watch it going down the track.
I watch it in the burnout box, but that's about it. I shift when the shiftlight comes on, or grab 2nd early to come down from a wheelie.
I will glance at it across the stripe.

A SS or modified4 speed drag race car is a little bit more of a challenge to look at the tach when shifting it, especially whne they have 5.57 rear gears and 2.98 first gear ratio in them
I've driven and raced 4 speed cars with a 3.09 1st gear with 5.57 rear gears with a 30 inch tall rear tire, I was real busy the first three hundred feet
I use to use a tach in the first 4 speed hemi car I raced, I was a lot younger then also, it seemed like it took forever to make one run, now it seems like they don't last as long now even with a new car that is a lot faster I guess what I'm trying to say is the more I drive race cars the easier and quicker it seems to go, and I can't focus as well as I use to

I look at it until I'm in 3rd gear, then I stare at the other car and the stripe.

I really like the shift light better for shifting. I really only look at the tach for staging.

My tach has a shift light option and I was constantly shifting late when I tried to use it. Maybe I'd have to set it up to flash some # of RPM before I want to shift, but then I'm already used to glancing down at the tach when I know the next shift point is coming anyway. I turned off that feature after finding no benefit for me.

I've told many drag racers who ask what RPM to shift at to shift the tranny when the motor quits pulling hard in each gear
I have over revved more than one motor trying to use a tack that was not reading the RPM dead on
If it doesn't seem right, it probably ain't

Haven't used one in years after I installed an air shifter and controlled it with the msd grid. The shift light tells me when the band or clutches are wearing or need adjustment.