Id recommend the siemens or hkc wireless. Both are 2 way but i find the siemens a much more flexible product. The enforcer is a low cost system with a since combined panel so on low end signalling is vulnerable to attack. Better stuff has a seperate end station which has the brains and signalling bits with a separate keypad. The only advantage to combining the 2 (as with the enforcer and the power max) is to save cost
Also ensure your chosen company can fully support the equipment. Anyone can fit any equipment but training and backup requires more than a passing knowledge