By that, I mean do they still have the fragile property, even if they don't break on a 1?

The Breaker Barbarian archetype gets increased damage when using a weapon that's broken, and takes none of the usual penalties. There's also multiple feats in UC that let you break a weapon on your enemy to confirm a critical, get them to start bleeding, etc.

Does this all synergize once a Barbarian Breaker has a +1 Half-broken Glued-together Shards of Glass Sword?

Depends on the weapon.

If the weapon specifically calls out that it's fragile after being masterwork on magical, then it's still fragile.

If it's made of a special material that grants the fragile quality, it retains that quality even if masterwork or magical.

It was my understanding that, if made masterwork, fragile weapons were no longer fragile.

It was my understanding that, if made masterwork, fragile weapons were no longer fragile.

It just seems like a waste to have two feats that only work on completely non-remarkable weapons. These feats and one of those bone/bronze weapons seems like what the Breaker was MADE for.

Weapons can break without being fragile. Even magic ones. They automatically gain the broken condition when they take damage equal to half their hit points, or when subject to a special effect that breaks them (like a rust monster or warp wood... or the new feats). Fragile weapons and firearms just have special rules which make them gain the broken condition easier than normal weapons.

Weapons can break without being fragile. Even magic ones. They automatically gain the broken condition when they take damage equal to half their hit points, or when subject to a special effect that breaks them (like a rust monster or warp wood... or the new feats). Fragile weapons and firearms just have special rules which make them gain the broken condition easier than normal weapons.

Unfortunately, both of these feats (Splintering Weapon, Disposable Weapon) require that the weapon have the fragile property. I would hope, personally, that even though a magic bone axe, or magic obsidian sword does not break as easily, that it still has that initial fragile property that would then make these feats usable.

Of course the weapons are still Italian.

Of course the weapons are still Italian.

Must be

I thought I recall hearing about normally fragile magic items being somehow able to lose their fragile trait due to some sort of magic addition?

oh right, it must have been from reading the description of Viridium:\

Viridium weapons have half the hardness of their base weapon and have the fragile quality. Viridium can be magically strengthened at an additional cost of +1,000 gp for a weapon or +20 gp for ammunition. This removes the fragile quality from the item but does not otherwise affect its abilities.

It only applies to Viridium RAW, but you could probably house-rule it for any fragile item (I don't really see many circumstances where someone would want to un-fragile a fragile weapon*; weight is an issue, but it's a minor one.

Aparently also:

Masterwork bone weapons[/armor] also have the fragile quality, but magic bone weapons[/armor] do not

*I guess crystalline (and viridium) are the two cases it might be desired. Adding only 1000g to make [true] crystalline non-fragile might be too cheap. (true crystalline weapons cost ~1000-3000+ gold)