Each of the links provided, and the Envirotech20 website, show each model equipped with a Fleck 5600SXT control valve, not a Clack WS1.
As I have not found any mention of the media tank sizes, based on the 2.0GPM drain flow rate specified for the ET42H system, that drain rate would be appropriate for a 9" diameter tank, which at 48" tall, will typically contain a maximum of 1 cubic foot (ft3) resin (32,000 grains total hardness removal capacity), not 1.32 ft3 (45,700 grains total) specified on the data sheet.
Likewise, the 2.4 gpm drain flow rate for the ET50H system, is appropriate for a 10" X 54" tank, which will typically contain 1.5 ft3 (48,000 grains total), not 1.56 ft3 (54,100 grains).
The unit which appears to adhere most closely to standard specifications is the ET64H system as the 3.5 gpm drain rate is suitable for a 12" X 52" tank, typically containing 2.0 ft3 resin (64,000 grains total capacity, not 69,300 grains)
While there maybe some variance in the total capacity between various brands of softening resin, the variance is usually modest, and so the controller will be programmed identically for the usual capacity as determined by the salt setting, regardless of the resin brand or stated capacity. (See resin capacity chart below)
To provide the best balance of useable capacity, salt efficincy, and water quality, an 8 lb salt dose per ft3 resin is usually recommended. As the chart lists the salt amount as lbs per ft3, an 8lb/ft3 salt dose will then signify 8 lbs total for a system containing 1 ft3 resin, 12 lbs total for a 1.5 ft3 system, or 16 lbs total for a 2 ft3 system.
To offer a marketing incentive for those models, I suspect each tank is being overfilled with some additional resin, but to do so, no bedding gravel is likely installed, thereby reducing the weight and shipping expense for each.
Bedding gravel is always recommended within a conventional media tank as it will optimize water flow through the resin, thereby permitting more of the resin's capacity to be utilized before hardness leakage occurs through the resin bed. In addition, the gravel will cause the resin to remain elevated above the bottom basket, so water will pass through additional resin before exiting through the bottom basket and up through the riser tube. Without gravel, the resin located within the tank's bottom dome below the bottom basket, will receive little to no water flow, so that resin will not provide much if any useful hardness removal benefit.
I have also not seen the cross link rating for the resin. Standard Cation softening resin is 8% cross-linked, but many big box and online systems are equipped with 7% or lower cross-linking, which will result in that resin being lower in cost, but providing a shorter useable lifespan.
When the water source is municipal, it will usually contain chlorine, so 10% cross linked resin will better tolerate constant chlorine exposure, but alternately, a backwashing carbon filtration system containing 1.5 ft3 or greater of GAC (granular activated carbon) media could be installed to remove the chlorine prior to the softener.
Many municipal water suppliers have been adopting chloramine (chlorine + ammonia) for disinfection. As chloramine is more aggressive and more difficult to remove than plain chlorine, it's recommended to utilize a filtration system equipped with 2.0 ft3 or greater of Catalytic Carbon prior to a softener. Without removing the chloramine, the aggressive nature of chloramine will more rapidly degrade any type of softening resin including 10% C-L, in addition to the control valve's soft internal components (seals, O-rings etc).
Either type of carbon media will also effectively remove/reduce many other toxic contaminants including disinfection byproducts (DBPs) including trihalomethanes and haloacetic acids, but the carbon requires sufficient contact time with the water to do so, which is why 1.5 ft3 is the minimum recommended quantity for GAC for modest water consumption, and 2 ft3 minimum CC media for Chloramine removal. With either carbon media, a larger quantity will provide increased contact time and/or higher flow rate support.
