"Do not use logical to check equations and inequalities that require simplification or mathematical transformations. For such equations and inequalities, logical might return unexpected results. For example, logical does not recognize mathematical equivalence of these expressions:
...
To test the validity of equations and inequalities that require simplification or mathematical transformations, use isAlways:

"isAlways(cond) checks whether the condition cond is valid for all possible values of symbolic variables in cond. If the condition holds, isAlways returns logical 1 (true). Otherwise it returns logical 0 (false)."