Not having a buckler in this game is a bit of a miss.
It's a pretty different sort of thing than what I usually think of with the regular shields. A buckler that was also a Medallion would be cool for an enchanted version. Might be able to use one of the monk's fancier punching animations for it or something like that? Using a buckler in actual combat would probably be closer to two weapon fighting with like a dagger anyway, than it would be to using a big tower shield. Instead of being worn on the back it might be worn around the neck or at the hip or to cover the loins. Or worn on the wrist like a gauntlet when it's not being used. Though the regular shield just sorta disappears anyway, so I wouldn't expect to see bucklers before we get shields on the back.
Main perk would be just that they look kinda cool and they were in BG1 as the only type of shield that could be used by certain classes - rogues and druids (I guess the latter just cause of the scimitars lol). The main thing about them is that they are curved, so could also double as some sort of ornamental bowl I guess. Probably a BG3 buckler would look like a skull just so it could match it's larger cousin. Even having one buckler on offer I'd probably be more inclined to use it on say a Human Wizard or Half Elf sorcerer or whatever, just because holding a giant shield makes every character archetype feel like some sort of paladin to me.
I enjoy especially items that recall the stuff we had in BG1, so things like Elven chain, Mithril mail, Ankheg plate are classics, bucklers and slings also fit the mold, but then for shields in BG3 they're all have very much the same sorta thing going on, even if they've got different looks. The basic shields I mean, not whatever extra enchantment specials. In BG1 we had the nice round buckler that had a few different visuals, the black and copper looking one, the shiny one etc. they all looked very much like bucklers. In BG2 all the shields had a look much more swoopy and jagged and in that game everything had spikes lol.
It's hard to imagine the Swashbucklers without the Bucklers.
The most familiar archetypes would be Zorro, Robin Hood, Sinbad and such, maybe something like this...; Which is the exact sort of absurdity I'm looking in a triple BBB game, just cause like a young Thulsa Doom, I mean right? lol Who knew!!! I little behind the times there with just the most ridiculous 70s vibes, but it definitely had the exploding barrels! And Geneviève is a badass - the lead probably deserved the Aradin treatment - Anne of the Thousand Days just decking that one. To think, she almost commanded Voyager too! Though if we're in the delta quadrant I'd still put my money on Janeway, she wouldn't have taken no guff from those buccaneers. Everyone could use a buckler though, cause you don't ever see em anywhere, here or there, maybe it's what's missing? Buckle up! hehe
ps. Random aside, but Buccaneer and Barbecue are related words, both on the slow roast. Has nothing to do with shields or bucklers there, but I just caught that, thought it was kinda interesting. Probably why we need all those smokepowder satchels and a free hand for the torches.
I'd say for BG3 the clearest call back would be The Princess Bride. Like going one handed just cause you want to do this RP... and most of the haircuts from the flick are already accounted for! Lol
That Rapier in Act III arrives so late in the game. If we got something like that a little sooner it would be fun to build around.