I agree, pulling one at a time worked for me. I think pulling all at the same time may be faster but pulling one at a time may be safer because you can react to each single strip as it tugs and releases and then tugs again. Just pull slowly and when it tugs (stops releasing) just maintain a slight tension until it releases again. At one point, one started to tear so I eased up and slowly continued with what was left and it eventually released enough so I could continue with the whole strip. Good practice for patience! XD
Be careful on this step: with my iPhone, one of the connectors (the home button/fingerprint sensor) was stuck to the underside of the bracket and I almost strained its cable.