1. Am I likely to be able to use this device or should I confirm it somehow by measuring my torso?

Most people who are tall, are also long legged. If this is the case, you will have no problem on the Pro Back Revolution at 6' 8".

Pro - Sitting in chair , measure the top of thighs to top of head. Top of thigh pad to floor on setting # 6, (not 7) is 44 inches.

2. Is this type of device as good at spinal decompression as the "back inversion tables" which hold at the ankle?
This is simply answered by saying ... Yes.

3. About how long is it okay for people to be in such a position (with blood going to the head)?

We don't recommend more than 3 minutes, although Studies have shown that maximum decompression is achieved in 70 seconds.