Daysy

A basal thermometer wrapped in an algorithm and sold at a flagship price, when a plain two-decimal basal thermometer plus a free charting app records the same temperatures and lets you or your practitioner interpret them. The single worst value in the category under a performance-for-money lens.

You pay several times what a competent two-decimal basal costs for a closed, proprietary algorithm tied to the company's app and servers; if support ever ends, an expensive device becomes a paperweight. Its headline accuracy figure comes from the company's own research rather than independent testing.

You pay a large premium for a proprietary algorithm wrapped around a temperature sensor, when a smart basal thermometer plus a free charting app gets most of the same insight; independent analyses have also scrutinised its accuracy claims, making the premium harder to justify.

Flagship money for an algorithm wrapped around an ordinary thermometer, with headline accuracy claims publicly contested by independent statisticians; it holds no placement in the dedicated basal-thermometer lineups, and What to Expect's current tracker guide names Mira, Tempdrop and Clearblue instead.

It costs many multiples of a budget basal thermometer while a cheap two-decimal thermometer plus a free charting app gets most buyers the same result, making it poor performance for the money by definition.

A premium fertility computer whose real product is a closed, proprietary algorithm, sold on effectiveness claims that have been publicly contested in independent reanalyses. Its main current endorsement is from a competitor's affiliate roundup, and the leading expert basal-thermometer guides do not place it among their picks at all.

The textbook case of paying a large premium for an algorithm wrapped around a temperature reading: a basic 1/100th-degree thermometer plus a free charting app records the same data. Its Trustpilot score of 4 out of 5 across 382 reviews is solid but unspectacular for a device at this positioning, and the heavily repeated 99.4 percent accuracy claim is marketing rather than a better sensor.

Flagship money for a closed fertility computer where a two-decimal charting thermometer plus a free app does the same job, and its accuracy claim reaches buyers only through a competitor's blog repeating manufacturer-linked marketing statistics rather than independent testing. The Easy@Home Smart Basal plus a free charting app is the correct purchase.