They may seem similar, but the Zarinaea-D is a Hakke, which means it only has 2 sight options, one of which will be a an iron sight. The muzzle flash on the Zarinaea-D is distracting, too.
The other thing is that Haakon's Hatchet has an aim assist of 79, compared to the 60 of the Zarinaea-D. Haakon's Hatchet sticks like glue to a target and is far more comfortable during gun dancing. Haakon's can get Hidden Hand to further improve this, whereas Zarinaea-D and other Hakke's cannot.
If you want a substitute for Haakon's Hatchet buy the vendor version of Dead Orbit's Paleocontact. Slightly lower range and aim assist, vastly better stability.
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That's all find and dandy IF someone is Rank 3 with Dead Orbit and has 150 Legendary Marks. If not, then what? One would have to... 1. Switch allegiance to Dead Orbit 2. Wait for Xur to arrive 3. Buy 300 heavy ammo synthesis for 101 Strange Coins 4. Make donation to Dead Orbit to reach Rank 3 Or... 1. Pay Banshee 2500 glimmer While it may or may not improve one's PvP game, it's a lot of fun in PvE. Either way, it's an overlooked weapon that I think deserves some attention.