with pretty much everything Rafe said above, especially the sentiment of testing our abilities 'cold'. I'm also not a fan of either the low ready or high ready as depicted in the video, with inertia leading to over travel & weapon retention being the primary reasons (although if someone is close enough to foul up your presentation, I'd encourage you to not have the gun out in front of you anyway). In addition, for the low ready I have the same issue that JustSomeOldGuy cited above regarding occlusion of the lower half of the visual field, however there's different definitions of what 'low ready' & 'high ready' means regarding a handgun. I've read studies by the Force Science Institute & other research organizations that define 'high ready' as having the handgun at full extension, but the gun lowered just below the line of sight, & 'low ready' defined as lowered at about a 45* angle. Using this definition, a Calibre Press study found about a 50% 'mistake of fact' error rate with the high ready (study participants using a shoot/no-shoot simulator shot a subject holding a cell phone); study participants using the low ready only had a 30% mistake of fact error rate. The low ready position was only about 11/100 seconds slower. The researchers pontificated that having just a fraction of a second more time to process the stimuli may have been enough to lower the errors by 20% (although fewer no-shoot targets shot, that 30% is still a bit disturbing to me).
I'm also not a fan of waiving the gun around everywhere my eyes go during the scan. Once I PID a threat, it's a matter of orienting my body & presentation of the gun so the sights instinctively go to where my visual acuity is locked on to. As shown in this video, it seemed like a range-ism vs a dynamic technique. After dealing with the initial threat, I prefer Sul for a 360* scan (mostly visual, but turning body as needed to complete the scan). The primary purpose of the 'scan', as I teach it, is to break the tunnel vision off of the work you just did so you don't get fixated, then answer the questions:
1. Are there more threats that need an immediate response? Or, potential threats to be aware of?
2. Where are my loved ones, & what is their status? Are there innocent third parties that need assistance?
3. Where is a better position to be, better than where I am right now, AND how am I going to get there? (Ie, not masking other people's fields of fire; looking for trip hazards before I sprint to better cover; etc).
((Note: these questions aren't always sequential; if there's another threat that needs to be maneuvered on, identify where you're going to go, & how you're going to get there to maximize cover/ concealment. "Remove the source of injury before tending to the injured")).
Going back to ready positions, I would think it prudent to differentiate between "training" vs "practical application".
In training, I typically start students with Position 3 of the 4-position draw stroke (some call this the High Compressed Ready, and while I'll use these terms interchangeably, saying "Position 3" is less syllables...). I'd describe Position 3 as both hands gripping the gun; gun close to the body somewhere around high sternum level with the elbows close into the side (anatomy & mobility of joints dependent); with muzzle oriented towards the target & barrel level/parallel to the ground. The general concept is to have the gun in the midpoint of the draw cycle, with the sights below the visual line of sight but ready to push the front sight into whatever point on the threat's anatomy your eyes are locked onto, and hone the presentation from Position 3 out to Position 4 (full extension), with the understanding that generally speaking you don't push to Position 4 until you are certain of justification & committed to taking the shot. After the student is smooth with 3 to 4, & 4 back to 3, we'll progress to starting from the holster (Position 1), & working thru the entire draw stroke.
Bringing it back to practical application, Position 3 can be modified with varying angles of muzzle orientation to prevent muzzling anything not needing to be muzzled.
For example, in the +/- 1 second it takes to draw the gun the threat makes better life choices & you deem deadly force is no longer 'immediatly' necessary, but you aren't convinced that immediacy won't return so you keep the gun in your hand. It's also useful while running with the gun in hand or pie'ing around corners/ threshold evaluations. I'm thinking what Rafe is describing as his CQB Compressed Ready is what I'm calling a variation of Position 3.
For turning 180* or maneuvering around other people, Sul is really good. Or, for retention when in a crowd, especially if the crowd is running away from a threat & you're trying to swim upstream against the crowd to reach the threat. ((Caveat: if the threat isn't really close, I'd recommend leaving the gun holstered vs trying to maintain control of your gun while moving in a crowd; there's so many things that could go wrong in that scenario...)).
I would add Temple Index to the list of ready positions, although I see it as limited to niche applications. ((Temple Index is a bit of a misnomer; I'd recommend having the gun further back than your temple to not block your peripheral vision. More like indexing the knuckles of your gun hand between your temple & ear.)) For an example use of Temple Index, if I had to engage an immediate threat on the front-passenger side window while I'm in the driver's seat, the Temple Index allows me a midpoint from holster to engage behind the passenger's head (controlling the passenger with my left/support hand so they don't get shot in the back of the head...). Another limited use of Temple Index is when opening doors with the support hand; at Sul the muzzle is pointed down so shouldn't muzzle the door hand, but if someone on the other side suddenly appears the rapid orientation of the handgun up to the threat often happens so quick that the door knob hand is still recoiling back to the body (or the person kinda forgets to pull their support hand off the doorknob...) getting muzzled along the way. Again, very limited utility in my opinion, but enough practical application for training on it.
Retention Position is another niche position. I don't teach it as part of the normal draw stroke, but as soon as there's sufficient distance from the threat the gun hand / support hand meet up near the sternum in Position 3, & the draw stroke is presented out if additional shots on target are still needed to stop the threat. ((By 'not as part of the normal draw stroke', I mean not like depicted in Mike Panone's book. That's may be how Mike learned it back in the day, but it's not what we teach now)).