(Note that the names of some of the strips are not quite as they appear on other listings, reflecting the choices of different translators.)
These albums collect a series of two-page strips that feature the misadventures of two young boys from Brussels going about their life, sometimes causing trouble, sometimes finding it comes to them. There's no ongoing narrative and instead each story is a self-contained gag. The two boys are prepubescent but otherwise of an indeterminate age that allows them to have broad appeal and fit into the week's gag. The other main character is a uniformed policeman though he isn't seen much here and the only name given is "Mr Policeman" when the boys write him a letter in "Happy New Year". He's usually identified as "Agent 15" and performs the traditional role of an authority figure who sometimes delivers punishments and sometimes gets caught out by the boys' antics. He also has a childish side to him, sometimes succumbing to the joys of catapults and yoyos, and he's not the only one of the boys' victims who take up toys against then.
In general, this series follows the naughty schoolchild trope in an urban environment albeit with some ventures out to beaches, the countryside and even further when the gag requires it. Although the fashions and technologies shown are standard 1930s, the humour in this strips hasn't dated. The only strips where the setting brings up a practice unfamiliar to me are "Festive Cheer" and "A Weird Story" which both feature the custom of celebrating New Year by sending a boy round to personally deliver little gifts to relatives and share a drink with them.
For the most part the strips here remain their own little world but a couple do break the fourth wall. In "A Serious Turn of Events" the boys and Agent 15 conspire to kidnap Hergé and force him to sign a confession that they aren't as portrayed. However, this turns out to be a metafiction in itself as it is shown to be a story written by Quick. The very last strip in Fasten Your Seat Belts shows the boys flying a home-made plane when they fall out and land on a cloud that slowly rains away... and they reveal to the reader "It's all just make-believe! ... You see, the cartoonist didn't really know how to finish the story!" But otherwise these particular strips don't show much of the fourth wall breaking that appears elsewhere in the feature.
Otherwise we have tales where the boys can suffer from either the typical, such as overconfidence on the football pitch leading to injury ("A Penalty"), the inability to get anything done because of others' music ("How Music Calms the Nerves" and also "Quick the Music Lover") or going out insufficiently dressed ("Proverb"), or else the extraordinary including accidentally swimming all the way across the English Channel ("A Record"), meeting the Loch Ness Monster who needs a tin opener ("Hard to Refuse") or digging all the way through the ground to a land of ostriches ("The Tunnel"). The strips in Fasten Your Seat Belts are slightly more down to earth than Under Full Sail but they both have their wilder elements.
There's very little political commentary on show here. "A Problem" does feature a Minister of Transport but it's more focused on the absurdity of some school maths questions and shows a bizarre solution to one particular one. "Pacifism" shows Quick opting out of playing soldiers but soon finding provocation leads to conflict. And "Naval Procurement" sees Quick and Flupke get into a competition with a little rich kid as they each keep bigger sailing boats in a comedic arms race. But otherwise this is a strip that's seeking to entertain rather than make more profound points.
Being a collection of straightforward gag strips with no ongoing narrative and no wider axes to grind, these albums represent Hergé's art and humour styles along with a degree of charm but little more. This is not a series to go hunting high and low for to have a complete set of all eleven albums with various translators but having a couple available is a nice complement to his other works and showing his range.