Hm, I had no problems whatsoever with the DLC and the merchant. Neither on Linux nor on Win10 (both steam).
The Belt is quite awesome for barb or monk retaliation builds - or anybody else who wants to use Firebrand all the time (6 uses/rest with Forgemaster Gloves - playing a melee cipher with it atm and it's awesome).
The Company Captain's Cap is one of the best (if not THE best) headgear because it has the highest stats boost of any headgear in th game and gives you immunity to mind control - pretty nice for priests or paladins. I used it on Edér lately with a duelist setup (rapier + dagger) and it's also one of two feathered hats that look good with such a setup and has bonuses.
The sabre is ok - Overbearing Wave on crit is pretty awesome for a rogue (works with Deathblows and so on) - pretty nice in combo with Swaddling Sheet and White Crest Armor - Overbearing Waves all over the place.
Fulvano's Blunderbuss is a bit meh. You need some shots in order to charm somebody (26% chance per shot). For example taking four shots can take an eternity to fire & reload in PoE with a blunderbuss. I don't know if it works with Powder Burns, but I doubt it. One could raise the chances with Driving Flight though.
I couldn't fully unlock the Spike-Flinger yet - Sagani is tryig hard but it takes a lot of shots to proc prone via spell chance.
The war club could be nice on a barb. Weaken/Hobbled with carnage, maybe together with St. Wygelt's Cudgel for a debuffing barb to carry over to Deadfire as Mage Slayer.
Besides that it's not too powerful. Lacks lashes as most other souldbound weapons.