I would be very surprised if the mechanical engineer that calculated the restaurant's expected water usage and therefore specified the plumbing system pipe sizes needed, had not also included specifications for an appropriately sized commercial softener. Not only is reducing the pipe size to connect a softener that is too small for the application not in compliance with plumbing code, a reduction creates a bottleneck, thereby making the engineer's flow calculations a wasted effort. As it appears 2" plumbing is installed, a 1.25" pipe section will not satisfy the same flow rate.
As the Fleck 5000 is equipped with only a 3/4" riser, there is a further flow reduction internal to the softener. That softener valve would be better suited for a residential application, not a commercial setting where high, short duration water flows are required on a frequent basis.
Suggest reviewing the original mechanical drawings and specifications as to the softener that was originally specified. There maybe cause for recourse against whoever was responsible for the inappropriate unit. As the piping reduction is not in compliance to code, at least that should have been caught during the mechanical inspection, even if an inappropriate softener was specified.
The brass unit is a thermostatic mixing valve, likely supplying hand wash and washroom sinks with hot water that is tempered to prevent scalding. See image at the bottom of page:
https://www.grainger.com/category/p...valves?attrs=Outlet+Size|1-1/4"&filters=attrs