Hi scrambler,
I would use “pressure imaging” or “pressure mapping” as an aide but not as a primary method of making a purchase decision. I would trust your body and careful and objective testing more than what the pressure mapping says. It also only measures the pressure on the mattress/skin interface and says nothing about the effect of pressure or stresses on the inner tissues of the body (which can be very different from the surface pressure) or about your alignment on the mattress.
In many cases in larger chain stores and with proprietary pressure mapping systems it is used more as a selling tool to “point to” only a certain line or brand of mattresses that are the only ones with information that has been programmed into the pressure mapping system (see post #2 here). If it can be used to choose between a broader range of mattresses or used to help build a custom mattress then it is more useful and could certainly be helpful but I wouldn’t use it to replace careful and objective testing for PPP (Pressure relief, Posture and alignment, and Personal preferences) or good judgement.
You can see some thoughts about some of the options that can help when a couple with very different needs or preferences in the first part of post #2 here. A side by side split is one of these and can be a very useful and valuable option when it is needed and available.
Phoenix