This advice all depends on how you use an item of course. Personally, I have praised this item as I use it in a completely different way. I put water in, once a month I take a TDS reading and it is around 10 usually. My tap water when I checked it today was 125 I think and the K19 at 14. My theorising. ends there! All I want to know is that the water I am filtering to put in to my coffee machine is of an acceptable quality and will not cause me scale issues in my coffee machine.
I expect to follow guidelines and change the single filter once a year and I am about to. My house drinks the water it produces and for £249 which is what I paid, I am quite delighted. I fully accept that there are other RO desktop systems around that produce better figures but why pay for them if your needs are simple as mine are. I believe another popular desktop machine is £495 on the manufacturers website.
The epitaph is, if you are a farmer and need a 4 wheel drive tractor capable of attaching a plethora of farming items do, a Fiat Panda 4×4 might not be suitable, but if all you want is to go to the shops once a week, a Lambourghini tractor might also be overkill!