The Zercher Squat and Deadlift are two of the most feared exercises in the fitness world. They are also two of my favorites because of this. Orginally invented in the 1930s by Strongman Ed Zercher, these variations are not for beginners. The fear of lifting with a "curved spine" is justified, but there is a big difference between thoracic flexion and lumbar flexion. The other issue is weight. I suggest starting out very light and increasing slowly, same as every new exercise, to ensure proper form.
The benefits to this hold are outstanding. It works the entire body and cardiovascular system. Not only does it force the spinal erectors and core to fight the weight, but it compresses the lungs at the same time causing a huge amount of internal pressure even in the standing position where most stop to rest on conventional squats.
I highly suggest working with the Zercher Squat before attempting the deadlift.