Reflex may state a setting less than 3.5 is undesirable, but @Horton is quite right. One needs to become very familiar with the Reflex "feel" and the way it functions and then set the release accordingly. It is prudent not using Reflex if one cannot get comfortable with this concept.
Very slight differences in the position of the release hinge, shell shape, spring tension, etc., make huge differences in the release force.
I set the two front buckles very consistently snug and dry land release before the brake strap becomes fully taught, and although the numerical setting is "~3", have yet to pre-release. I do release easily with too much tip, but appreciate the no Achilles stress after having blown it out in 2013. The brake strap will engage prior to over-flexion of the ankle too, so I do feel it protects the Achilles (@Than_Bogan) in this regard, again assuming the tension to release is not too high.
Don't just bolt on a Reflex binding to your ski until you become very familiar with how it functions,