firstly i have to say i have a slight vested interest, my father in law runs a business called aquasoft- and guess what he designs makes and retails water softeners both domestic and industrial units...
when i moved from the lake district where we had naturally soft water i was surprised how quickly my kettle furred up when 'down south'... i then got involved and eventually married SWMBO and i found out the low down on water softener sytems....we have now had one for over 15 years...
i also found out those systems that work well and those that have impressive claims but do very little, ( ok they do a bit but they certainly dont soften all your water )
my honest opinion is the magnetic types are all 'hot air', they simply dont do much, they dont remove or break down large amounts of calcium/ lime from the water... then there is the unit that clamps around the pipe and then you connect it to the house mains electricity, these are similar to the magnetic ones but your electric meter spins too !!!
in the links in the original post there is a 'whole house 2 stage filration system' - made by culligan, this is a filter, these filters need changing ever 6 months or so...they trap the waterborn particles, they dont eradicate them, just filter them ( see this as a giant brita filter ! )
then there is the water powered softeners that use salt, - salt is the medium which is used in regeneration of the softening medium...these are ok, these can work if the water pressure in the area is ok, - they are very similar to the systems described below apart from they use the water pressure alone to move the moving parts...
then there are the water softeners which are electrically powered which soften your water through ion exchange resin, the hard water and its impurities are attracted to the ion exchange resin they pass through, once the resin is saturated with calcium then the water softener needs to 'regenerate'....
this is done by the softener making brine - this is mains water with salt in it, this brine is then pumped into the ion exchange resin, the salt in the brine breaks down the calcium and the impurities from the resin, - the resin is then backwashed and cleaned and all the nasties in solution are pumped down the drain, the water softener is now regenrated and the resin is ready to go again....
the big question is do you want a fully automatic water softener ( usually more expensive) or a timed softener,(the automatic one is screwfix item no 45007) the fully automatic version is exactly that, the water softener is plumbed in and there is an internal counter that knows when the flow through the unit has caused the resin to reach saturation... it will then also automatically start the regeneration process so you maintain soft water supply....if you dont use any water as your away the unit stays idle, if you use lots more water then the unit regenerates as required...
the usually cheaper version is the 'metered/ timed' version ( screwfix item no 80208) which relies on a manual setting, this is manually set to regenerate at a pre determined time set on a dial, this means that if you have visitors and use alot more water you may exceed the softeners capability, or if you are away on holiday and use no water in a week the automatic dial will regenerate the unit even if its not needed....its just a time setting ... its manual and basic but if your water consumption is pretty steady this unit may be ideal.... the timer is usually set to regenerate in the middle of the night when water consumption is low.
there are several fundamentals to understand prior to having any kind of water filter/ softener installed
the first is simply why you are having it fitted...how much water do you use and does your water consumption fluctuate massively ?
artificially softened water is ideal to protect your washing machine, your boiler, your steam iron, kettle, bathroom fittings/ plumbing and all that stuff from build up of scale...
its not recommended for powerdered baby milk, plants in the garden and some dehydrated food stuffs, - by law you must have at least one remaining hard water tap in the house,
consider how much water you use... the units in screwfix ( used as an example) are relatively small units in terms of capacity, the litre quanitities quoted are the resin tube capacity, the bigger the resin tube the bigger the capcity to deliver the soft warer required....
a small unit may be fine it may just have to work flat out and regenerate more often to keep up with the demand for soft water....
we were advised to use a 12 or 14 litre unit for a family of 4 using in an average sized house using a fair amount of water...
our unit is fully automatic and it regenerates about every 10 days , during each regeneration it uses approx 7lbs of salt
take into account the cost and amount of salt you will use, this is usually alot less than ceramic cartridge filters often sold as scale reduction systems sold by the DIY stores, these filters need changing twice a year, and if they saturate prior to replacement you get little protection
as for further advice beofre comitting yourself look for a member of the british water association or a member of the quality water group- ask advice and definately consider all the options but if you want to remove rather than filter the calcium and lime then a softener not a filter is the best bet....
as for which softener -then there are alot of units out there that all do the same job-
look for a qualtiy valve head, (autotrol are good ) - look at which unit fits if its going into a kitchen cabinet- there are compact units out there-
look at the salt type they use , some use solid blocks of salt that fit into a casette, these are compact and tidy but expensive to buy blocks of salt compared to tablet salt or granular.
any questions, just ask....