Why users don't buy a €60 add-on — and how one simple explanation raised revenue per user by 8.5%

ALB Filter sells drinking water filters for home and travel. The online shop is optimised continuously.

Together with Heinrich Mahr, I help them test the right things.

Instead of jumping straight into experiments, we run an exploratory user test. Users are asked to visit the site, find a product they like and buy it.

The goal is to better understand how users orient themselves on the site and how they make decisions.

On top of the main filter, users can buy a pre-filter (Protect) for €60 that extends the product's lifetime. A high-margin add-on that is rarely bought.

In the user test we keep observing the same behaviour:

Users open the product page, run into the choice between “with Protect” and “without Protect” and wonder what that even means.

The add-on is not explained at all in its immediate context. One user even assumes it is an extended warranty rather than a physical product.

The information does exist further down the page, but most users never see it.

Internally it's perfectly clear what “Protect” is. For the user, it isn't.

They're asked to make a purchase decision without understanding what they're buying.

At the moment of decision, users lack context. So we give them the information exactly where the decision happens: we add an info icon plus a modal with a detailed explanation.

People don't make decisions about things they don't understand. Instead of testing new things, it often pays to first check whether the offer is even clear.