Once you put someone in handcuffs, their safety becomes YOUR responsibility. This does not apply to LE, but to civilians. Means you cannot harm them, and you must prevent them from being harmed while they are cuffed.
WRONG!!!!! Even when I'm on duty, the moment I handcuff a defendant (BG), he is MY RESPONSIBILITY, and I face the same criminal/civil liabilities as any other LEO OR CIVILIAN would, should something bad happen to him/her while in my custody.
But none of the possible legal ramifications are my reasoning behind NOT cuffing him, even though I do own handcuffs and are properly trained in their use. My reason is that I'm not going to subject myself to further risk and/or subject my family to further risk my placing myself in a situation where safety is compromised by getting too close to the subject.
Even with my better half being ex-military, and having the mindset and skills to cover me, her possible nervousness and "adrenaline rush" while holding a gun in her hands to cover me while I'm restraining the subject (not to mention she would now have ME and SUBJECT within the line of fire) is again....not a risk I'm willing to chance for either her, myself, or the kids.
Again, this is just my opinion on the matter. Whether you actually do cuff a subject is probably going to be more dependent on the situation. It's very easy to sit back and play Monday-Morning-Quarterback here and judge on a situation most of us have never been in and probably never will be.
All that said: As far as whether to use flex-cuffs or standard steel cuffs - I'd prefer standard chain-style cuffs. A prepped flex-cuff consists of two loops which need to be slipped over the BG's wrists, where as a standard handcuff can be applied directly against the wrist while I have a grip on his fingers and hands and lessen his chances of swinging an arm/fist at me.
Shoot well, stay safe, and stay healthy,
38SnubFan