Measure fit instead of relying on a label
Check wrist fit when choosing a watch and the dimensions of devices you carry when choosing a backpack. The Thule Subterra 2 21L has a specified laptop compartment; compare that space with your laptop's actual dimensions, including any case. A screen-size label or a bag's total volume does not settle whether a particular device fits.
Separate watch versions and battery modes
Distinguish the Garmin Forerunner 165 from the 165 Music. Check which phone and features you intend to use; do not assume the standard model includes the Music version's storage functions. Battery figures for smartwatch use and GPS use describe different modes. Choose the mode relevant to your trip when comparing the manufacturer's estimates.
Check trip constraints and the exact bag
Compare the same backpack volume and model code, and measure its external dimensions against the carrier's current limits. Water-resistant fabric is not a guarantee that everything inside will stay dry. Confirm the pockets, luggage attachment and included accessories you need. Keep watch extras and bag contents separate from the base product when comparing offers.
Further reading
A new product should solve a clear problem or add something useful to your day. Check the exact specifications and compatibility before spending.