With the advent of the FotM SAM, this piece has sort of become a rallying point for identifying SAMs who don't know what they're doing. It's typically cheap and looks kind of neat, but it's massively inferior to Haubergeon for TPing, so bad SAMs who TP in this tend to stand out like sore thumbs.
However, I think the Hachiman Domaru itself kind of gets a bad rap that it doesn't totally deserve, thanks to this stigma. It's true that it's only a step above being naked while TPing, but it's actually comparable to Haubergeon for WS, and in some early 75 builds, wildly superior. Let me explain.
To start with, the offensive stats during a WS are comparable. -2 accuracy is not going to completely break you with the Y/G/K accuracy bonus, and the 10 attack of Haubergeon is generally understood to translate into less damage on those WSes than the 3 more STR of the Domaru. So that alone makes Domaru defensible as a WS piece, but the real strength is the Store TP.
I said this was a superior WS piece in "early" builds, because the necessity of a 6-hit Store TP build means SAMs don't really get a ton of gear flexibility until they get a Rajas Ring. Before Rajas, you need several pieces of Hachi gear to cover the gap, and for most people not using Shinimusha Haidate, this will mean full-timing Hachi Hands and Feet and Chiv Chain with 5/5 Store TP Merits.
What Domaru does is let you pull one of those pieces out during a WS, namely the gloves. Considering Pallas Bracers are extremely cheap and Alkys are no longer so expensive as to be unattainable, Haciman Domaru ultimately means somewhere between a +8 and +11 Strength bonus for a Rajas-less SAM. Since SAM WSing is basically all about stacking as much STR as possible, this is pretty significant.
So yeah. Domaru's a great starter WS piece for the SAM who just hit 75 and is starting to expand his WS gearswaps. It remains a TERRIBLE TP piece and it kind of falls by the wayside once you get a Rajas Ring, but it doesn't deserve the scorn heaped upon it.