Does the existing system have a door restrictor as part of the Montgomery clutch? If so, you could probably get away with a like-to-like replacement; however, if it doesn't the Wittur products I mentioned above are the best solution.
The main reasons I'm a Grinch of harmonic door operators is as follows:
1. The dangers of the gate switch. They can get inadvertently or intentionally pressed, compromising the safety system. Not all jurisdictions require DLM. Even with DLM, it can still be problematic. The lift could go out of service trapping people on upper floors who can't walk stairs. The new-style linear ones have cabin door interlocks (no gate switch), making such situations impossible. Here's an ex. of what I'm talking about.
https://www.youtube.com/watch?v=AEOkZDBCDiwBeing able to spit the door at floor level is also bad. Pranksters are capable of manually separating the doors compromising the lock system. This can also happen if a spring is weak and the door strikes an object.
2. With the presence of interlocks, restrictors are no longer necessary. Harmonic operators do not support cab door interlocks and many types of restrictors can easily be disabled/bypassed by mechanics compromising passenger safety. Worse yet, those electronic restrictors like hatch-latch by Adams can fail in the locked position and are prone to sensor misalignment and dead batteries during power failure. These were responsible for many fatalities at WTC on 9/11. On new installs (especially all glass), no ugly expensive sheet metal is needed between floors.
3. During entrapment, Harmonic operators can become self-locking (operator can move the doors, but doors cannot move operator). This situation requires rescue workers to have to get on the cab top and spin the infamous wheels, this can be problematic in situations where the lift is on the top floor or in the case of a steep drop (i.e train station, garage). Linear door operators never become self-locking. Once interlock is released, door can be manually opened from both floor level and cab top. Also, if lift stalls at floor level, no triangular or drop key is needed due to the spring loaded clutch. All you gotta do is push open the door. See examples below.
Self-locking ex. GAL:
https://www.youtube.com/watch?v=9TnHnKU9EnQSelf-locking ex. MAC (0:36):
https://www.youtube.com/watch?v=TcdMfuUJprk Linear difference:
https://www.youtube.com/watch?v=eyjQC7llJkE4. Use of Harmonic operators on full glass door panels is not only more expensive due to construction costs, but a fall hazard for mechanics. Operators propped up on pedestals pose fall hazards for workers due to a steep drop from the operator to the cab top. New-style linear operators eliminate this.
