Double shotties do two sequential hits. It was like this in 0.9.9 and before, and Thomas reminded me of this fact only the other day - I'd take Thomas's word on it alone since he's a great source, but if you wanted additional confirmation check the wiki screenshots I posted, or check ingame - you'll be able to tell in command mode and by the knockback.
I feel like there should be more "Unique" master assemblies, where it requires a specific item and makes a specific item, like Ripper.
I also think that, like, some of the assemblies just look useless on paper. Tactical shotgun pretty much is THE shotgun except for some circumstances (Uniques, Elephant gun on some builds).
Whew, wanted to wait for someone else to say something controversial since I knew i'd take a lot of flak for it!
I agree but on a slightly different point, if that makes sense. Rather, I think that some of the assemblies are too "expensive" or "rare", rather then "Useless'. The first thing a lot of people would call "Useless" would be the chainsword (Knife + PB, Knife becomes 8d2 and +1 accuracy), but it speeds up a knife run by a LOT, i'm guessing.
The Tower Shield (Red Armor + PO) gives a whopping 12 protection, but has only 150 durability which is eaten through quite fast due to the lack of resistances - which can make even the common green armor useful nowdays. It seems too little benefit for an Onyx mod pack - Those are quite rare and you could make a very arguable case for simply using the onyx on a red armor and ditching other armors to have more inventory space to facilitate healing/tactics/more dakka. It also cannot be repaired, meaning those little armor shards won't do anything for you. The -50% movement speed just seals the deal.
Another is the Cybernano armor (Armor + PPON, Original Protection + 4, infinite dura). Requiring not just 1, but 2 rare mod packs, and is cursed. The effect of this assembly could be mimiced by simply PPO, as Whizkid 2 will allow that for you. It also doesn't make it cursed. The only benefit that the Cybernano armor holds over Armor + PPO then, is the ability to have the finished assembly modded once more with a modpack - Meaning to get the benefits of the cybernano armor, which arn't really that great compared to PPO or even a nanofibre armor (Armor + PPN, Original + 25% all resistances, Cursed, indestructable, regenerates), you have to use a whopping 5 modpacks. That's not practical outside of Ao666, and even then there's better options.
Double Chainsaw (Chainsaw + PPB, Chainsaw becomes 8d6, loses two accuracy) shouldn't lose two accuracy. Might be a moot point since Brute gives melee tohit, but it just doesn't seem right.
You should also have a small chance, one every 20 hits, to go berserk with it equipped because YOU'RE A MAN AND A HALF WITH 2 CHAINSAWSEnvironmental boots (Boots + PBT, +75% lava/acid, Caps at 90%) should be buffed a little bit, if you're applying something that's not A to boots you should reap the rewards. Make it 95/99% or something like that, or remove the -25% speed penalty. Also, this could use some tweaking:

It should just have 200% dura and +2 protection period, unless there's an issue with coding and that's understandable.
And those are a few examples. Will pause to let others have their say though =o