I decided to make this as it is my favorite set of weapons that doesn't get enough love despite its faults, so I'm making this post as a mini-review/guide of it and how it works, with my own tips regarding its use for other knights to try out. Shoutouts to @Jcyrano for giving me the idea :D
If there are any other Torto users who want to share their own tips and experience with it you're more than welcome to post.
The very first thing one must know about the Tortofist is that it's anything BUT a gun. It relies on gunner stats, but functionally? the best way to describe it would be a sword/bomb combo, so you have to think of it as such when using it. While other weapons focus on two or very rarily three types of damage, the Tortofist covers ALL types of damage including normal. So you can choose whatever fits the map, given that you DO have all four of them that is.
----- Main Mechanics -----
Light attack is a combination of various aspects of different swords. Flourish-like movement, 2-hit combo, knockback, and a somewhat weaker (still debating on this one) stagger of Sealed sword/Troika. It also shoots a projectile with each lunge, dealing more damage than the initial swings but less range than majority of guns, somewhat resembling the 4/5* spur-line swords.
By basically being a sword in function, you can apply all sword tech in the same manner- like Shield cancel for fast hits and repositioning or holding a charge to extend your combo due to the high knockback.
There is a flaw though. With the Tortofist being a gun, that also means it has a reload animation, meaning that completing a combo also has a lot of downtime if you don't have a high enough ASI to counter it. So the best way to use it is to poke at things with Shield cancel and use the full combo if you need to stagger/push away if necessary.
Charge attack is the Star of the show, it fires high damage shards around an area, dealing an extra for the contact damage of lodged shards on the ground. If we translate the time it takes for the shards to fall it is, in essence, a RANGED. BOMB. Do have in mind that it has a hit limit for both the shards themselves and their contact damage, with a maximum of 3 hits of each per enemy.
Another special aspect of it is that it works as a dodge. After firing it causes a lot of pushback, which you can use to run in the middle of a group to center the shard spread and quickly get out or bait an attack and have the shards hit dead-on while the enemy is on downtime.
You can also Shield cancel the animation after firing, which lets you both reposition with a lot of speed and "Chain" at high CTR, effectively letting you trap big mobs in a spot if possible.
It does come with some caveats: Firstly, it fires an invisible, non-damaging "shot" that dictates how far the shards will travel, once it reaches it max range or "hits" a target, the shards will spread from that spot. This shot can also trigger the projectile response AI some enemies have, meaning it depends a LOT on both adapting to every possible enemy combination and free-aiming, requiring a lot of skill and positioning to hit as many enemies as possible.
Secondly, the shard spread is completely random- which is both a blessing and a curse: You can get a good spread and hit a lot of targets within an area. You can get a focused spread, practically obliterating anything within that zone... Or you can get cursed by the tortodrones themselves to miss almost every shard.
Thirdly (and I need some bomb mains to corroborate me on this), the shards themselves are similar to those of the shard bombs: If there is no spot for the shards to fall (E.G. a super tight pack of mobs) they will despawn or fall right in front of the group, they also have the tendency to avoid walls and fall away from them.
As Gunner main myself, the main purpose of the Tortofist is to provide AoE burst damage, letting you hit multiple enemies whereas with most weapons you can only target 1-3 at the limit aside from some exceptions but are just as limited. Autogun-line only hits those at front, Magnus-line hits in a straight line, and Catalyzer-line needs a lot of build up to rack up damage. A good combo with the Tortofist is the Pulsar-line, as you can shoot a group with a charge and push back any enemies that got out back into the already lodged shards.
The Tortofist excels dealing high damage to a whole group in a short time-frame, letting you pick off stragglers easily with your other weapons once they're low.
In some cases, both the knockback and pushback can be a lifesaver to get out of sticky situations, do be careful about sending yourself into traps by accident though.
Hybrid builds can benefit just as much, by combining the Tortofist Charge with swords like the Brandish-line or Sealed Sword/Troika-line that have a lot of knockback, you can aim behind enemies to set a wall and quickly swap for a quick charge or light attack and push mobs into the shards for stacking damage.
Other Torto users can also send staggered enemies from the shards right in your direction to finish off or blast away with a charge if it's ready or place a wall between you and a mob if you're getting overwhelmed.
Bomb users can also make great use to both themselves and other Torto users, Status bombs greatly or completely impede movement, letting you and others to shoot charge attacks in convenient spots for maximum damage. Vortex bombs and Tortofists are an absolute combo; on maps with set spawns you can set a Vortex and launch a charge into it before a wave spawns, hitting every enemy caught in the vortex before getting swept by the contact damage. You can also group them up in a singular spot with blast bombs to fire away directly with a charge once in position.
Overall, the Tortofist while being a decent to great weapon when you learn how to use it at its best, its greatest strength comes when combining it with other weapons to make use of both the damage dealt from the shards AND consequent contact damage, aiding your team by blocking waves of enemies from rushing or make use of lodged shards.