Which of these is actually sized to fit under an airline seat?
Based on titles alone, the BAGSMART and MATEIN packs make explicit personal-item claims. The Tortuga's 27-32.5L range and carry-on framing suggest it may exceed typical under-seat limits on some airlines, and the Osprey's listing doesn't address airline sizing at all, so you'd need to check dimensions directly before flying with it as your only bag.
Is 35L too big for a personal item?
It can be, depending on the carrier. The BAGSMART listing calls its 35L bag airline-approved as a personal item, but airlines vary in what they enforce for under-seat dimensions, so that claim is worth confirming against your specific airline's published limits rather than taking the liter count alone as proof.
Can the Osprey be used as a flight bag even without an airline claim in the title?
It's plausible, since it's framed as an everyday commuter and campus pack with laptop carry, and many daypacks of that description do work under a seat. The listing simply doesn't make that promise itself, so you'd be relying on your own measurement rather than the seller's claim.
What's the difference between the Tortuga and the two dedicated personal-item bags?
The Tortuga is titled as an expandable carry-on running up to 32.5L, positioned as an airline-approved carry-on rather than a personal item specifically. The BAGSMART and MATEIN listings both lean into personal-item language directly, suggesting they're built with under-seat use as the primary intent.
Does a luggage strap or laptop compartment change how these compare for air travel?
Those are convenience features, not sizing claims. MATEIN's luggage strap helps it stack on a rolling suitcase, and all four listings mention laptop storage in some form, but neither feature tells you whether a bag fits under a seat — that comes down to the stated liters and airline-approved language in each title.
