you mean the ones that look like expresso machines? Not worth the money and you are depending that Hagen will keep producing the exchange cartridges. Absolute gimmicks. I had a discussion with my local rep re. the water change indicator. Turns out TDS are measured since nitrate in the water increase the TDS count. However, harder water already has a higher TDS count. Keep things simple. I have some Eheim classics running for over a decade.
With sterling where it is against the Euro at the moment it pays to order online. I'll send you a pm where I found the cheapest filters
