By definition, if you use a different release you are using a different technique. If you have throw away prior to impact - you don't have a flat left wrist. If you change that on the next swing to have a flat left wrist - guess what, it's a different technique. And btw, if a flat left wrist was all you changed, you wouldn't be hitting the same flop shot. A flat left wrist with a square clubface would not produce much of a flop at all. So not only a different technique but also a different shot.
Now you are trying to redefine "throw away" and "flip release". You can have a lot of throw away and a flip release but still have a flat left wrist right at impact or a little beyond. The critical element is that the clubhead is speeding up while the hands are slowing down. You can vary how you set the clubface and how much you release the right wrist to suit the shot and conditions. Each specific combination is part of the same technique, not a different technique.
Mickelson's technique in the video you provided as a definition of the "flat left wrist method" had the arms and club both accelerating through impact, which would be a very different technique.
BTW, I bet I can hit a very soft shot with a square face and flat left wrist at impact (but bending immediately afterwards), just not as soft as one hit with more flip before impact and an open face; however, I'd need a good lie to do it.
BTW, I wasn't using a square face on that shot, and don't normally on a flop shot. A different technique that Utley teaches combines a square face with a left wrist that is cupped at address and throughout the swing. I can do it in practice, but it feels awkward. I prefer the flip release I worked on with Brian.
How the club reacts with the ball says everything about the result you get - the rest is show biz and style.
Funny you should quote Brian here because he is the one who taught me that you should judge the quality of your short shot technique by how the club reacts after impact: up the right arm at waist-high on a mid-sole pitch, above the right arm on a back-edge lob, below the right arm on a leading edge pitch.
The club will pass the hands in all shots as the right wrist straightens which means with a wedge, iron, hybrid, and driver. The question is, does it straighten before or after impact.
No, that isn't the question. The question is how fast the clubhead passes the handle around impact. On a lob shot, you want the clubhead to be moving faster than the ball right after impact, which means the hands will have almost stopped. The left wrist condition AT the instant of impact does not make this happen, BUT trying to maintain a flat left wrist condition THROUGH impact, like Mickelson demonstrates, would prevent it.
Why are you making this soooo hard?
I'm not making it hard; you are. Just admit you are wrong.
If he has left wrist bend at impact - guess what....(wait for it).... he's NOT hitting a flat wristed flop.
But you told me that he only hit flat-wristed flops, accelerating the arms and club through impact, and linked to that video as proof. It's nice that you've changed your mind.
Because the high speed video I used in this thread was not available then, and that was the only decent flop footage I found on Youtube at the time.
What this guy is doing is completely different from what Mickelson describes in your video. If you're now saying that what this guy is doing is your preferred technique to hit super high, soft lobs, then I agree, and it is the same technique I use.
No one's claiming a hinge and hold is the way to do it, but it can be done with a nice flat lead wrist and open club face. 
