I'm playing my first 11-20AP, so I'm reading up on some of those high-lvl options.
If I'm reading this right, the boulder is created and displaces the primary target with no strike hit requirement. Though you will not get the damage, this seems a great tool due to the reliability provided by functioning on miss.
As someone who throws down Holly Bush Feather Tokens for instant cover, I also anticipate the 5ft cube being able to serve double-duty for that purpose.
https://2e.aonprd.com/Equipment.aspx?ID=1903
Boulder Seed
Item 12+
[Alchemical] [Bomb] [Consumable] [Splash]
Source Treasure Vault pg. 44 1.1
Usage held in 1 hand; Bulk LActivate [one-action] Strike
This bomb is made of volatile fluids that rapidly expand and harden when exposed to air. A boulder seed grants an item bonus to attack rolls and deals bludgeoning damage and bludgeoning splash damage, according to the bomb's type. When activated, the bomb fills a 5-foot cube with hardened foam, which has stats according to the bomb's type and which pushes a primary target of a certain size or smaller occupying that space 5 feet away from you. On a critical hit, the target also falls prone. The splash zone fills with rubble, creating difficult terrain. The “boulder” the bomb creates fails all saving throws and loses 1 Hardness per round, disintegrating into fine powder when the boulder's Hardness is reduced to 0. At that time, the difficult terrain the bomb created also disappears.
Boulder Seed
Item 12
Price 360 gp
Bulk L
You gain a +2 item bonus to attack rolls, and the bomb deals 3d4 bludgeoning damage plus 3 bludgeoning splash damage. It creates a boulder as hard as wood (Hardness 5, HP 20) that pushes Medium or smaller targets.Boulder Seed (Greater)
Item 18
Price 3,600 gp
Bulk L
You gain a +3 item bonus to attack rolls, and the bomb deals 4d4 bludgeoning damage plus 4 bludgeoning splash damage. It creates a boulder as hard as stone (Hardness 10, HP 40) that pushes Large or smaller targets.