Pros:
-Costs slightly less than SPG-23.
-Can attack over buildings.
-Siege Shells are cheap.

Cons:
-Lower speed than SPG-23
-Slow projectile
-Low rate of fire
-Less range than the SPG-23 mod-A
-Less ammo variety when used with modded ammo. (See: Rampant Arsenal, Warheads, and True Nukes)
-Ammo stacks up to 25 shells.
-Grenade-sized explosion

Conclusion:
It's a discount SPG-23.

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You're extremely right.

The main idea was: even a combat-buisy, "not efficient", factory designer can unlock it "fast". Not much tech needed, not much resource flow needed.

Handcraft 4-10 of it while doing "else" (or setup a production).
Setup a shell prodction, that a poor resource flow can handle.
Feed shells to it with support units (hauler, almf, warden, else)
Form a group (robots, smg armor) of units to shell some worm-infested nests that would, otherwise, cost severe losses to attack without it.

So, it is supposed to be the earliest available, shell-wasting-if-not-supported, primitive siege tool.
If it gets too good - the main idea will be lost.
If the biter nests are weak enough and/or your advance goes fast enough - may skip it.

The feedback you gave is the one i was dreaming of. Thank you x)

Will think of how to give it a better use (custom shells with multiple actions, probably).