Dazed, Gary Slusser's points on the Clack WS-1 are technically correct. It is a more versatile control valve. Two points: the versatility is not a significant advantage to most homeowners who only want a reliable, family-sized unit, and don't need 5-7 cubic foot capacity (commercial size).
The Clack WS-1 can be used on tanks from 6" to 21" (max 7.5 cuft), the 5600 in any version, 6" to 12" (max 2.0 cuft softener). My largest residential softener, a 5.5 cuft. A 2.5 or larger bathroom house with body spray showers and large soaking tubs require much larger softeners than most dealers realize or sell.
The features of the Clack WS-1 are; simple and very easy to repair and program, lower priced and many fewer parts, variable reserve, soft water brine refill, the meter turbine comes out the side rather than having to disconnect the control valve from the meter if there is a problem, all the seals and spacers come out of the Clack as one piece. Fleck's seals and spacers are separate parts (9-12 separate parts) and most Fleck valves will require special Fleck tools to get the used seals and spacers out and the new ones in. The Clack WS-1 has both delayed (to like 2:00 AM etc.) and an immediate regeneration if the gallons meter zeros out at any time of day or night, after no water use for 10 minutes. The Clack has much more history and diagnostic info in the computer than in the new Fleck SXT timers, there is no separate cam operated brine valve on a Clack as there is on all Fleck valves. The version of the circuit board I use in the Clack WS-1 allows for wide flexibility in changing the length of time the various cycle positions run for (backwashes, brine draw, and final rinse). The 5600 without the new STX timer doesn't allow that.
The Clack WS-1 is head and shoulders above all Fleck valves except the 6x00 or Proflo. Otherwise only Fleck's new SXT timer allows for some of the features of the Clack WS-1. The other Fleck timers/powerheads have none of those features.
... The second point is that.... the Fleck will be much quieter in its operation. Clack uses a camshaft and spring-loaded gates that open and close under pressure to direct its water flow, and they tend to slam shut with a resounding, pipe rattling thump as the valve progresses through its stations. The Fleck uses a piston that moves vertically between stations, closing off flow gradually, so instead of a 'clunk' you get a 'hiss'. Both are good products, quite suitable for residential POE water treatment.
Wrong, you are confusing the Clack WS-1 with GE/Autotrol valves.
All GE/Autotrol control valves have a camshaft and spring loaded flapper valves. No Clack control has a camshaft or any springs; only a piston running in seals and spacers that all come out as one piece by pulling it out with a curled finger in the hole the piston came out of.
Clack has improved the Fleck seal, spacer and piston design. The piston in all Clack valves goes in/out with a screw drive, not the drive wheel and connecting rod/bar Fleck design that causes side force wear and then leakage of the piston stem oring and Teflon coating on Fleck pistons and their stems; on their brine valve also. There is no Teflon in any Clack valves. The 5600, 6600, 6700 Fleck valves have the piston going up/down but all others are in/out but all Fleck valves have a drive wheel and drive connecting rod/bar design; except for the SXT version. Clack does not, all of them have a trouble free screw drive for piston movement and it uses only three small gears in addition to the motor gear.