I've played about 6 forts into the 5th year or farther(vanilla with my own little tweaks). In that time, ONCE the humans brought a wagon. I was so excited! The following year, they did not bring a wagon. I died a little, inside.
The arsenal dwarf works.... but there's issues. I've gotten used to the quirks, so I know what to do and what not to to make the system "work."
1) Never ever ever ever assign dwarves a "class" of weapons. Always use the 'assign specific weapon' option. This is a giant pain in the ass, but it prevents dwarves from carrying around 8 different weapons. Classes of armor is fine, just not weapons.
2) Unless you are using the 'replace clothing' option, NEVER assign clothing as part of a uniform. This sometimes causes dwarves to drive themselves insane trying to put on mutiple pieces of mutually exclusive clothing.
3) If you do use the replace clothing option, its ok to put clothing in the uniform. But when dwarves go off duty, they will sometimes drop all their clothes on the ground in a pile and strut around naked for no apparent reason. This can be kind of annnoying, as it creates tons of extra hauling jobs.
4) If you need your military in action RIGHT NOW, make sure you halt all production of weapons and armor. There's a bug where every time a piece of armor is created that's eligble for the uniform, 90% of the militia will run over to a stockpile, drop a piece of armor and pick it up again. This also happens with weapons if you don't use 'assign specific weapon.'
5) If you need your military in action RIGHT NOW, try to occupy your arsenal dwarf in some way so he doesn't give equipment upgrades in the middle of a fight. This can be...FUN.
6) always use the 'Exact Match' equipment option. This prevents militia from being assign items that do not belong to you, and helps reduce the amount of mid fight scrabbling for equipment that happens further.
Unrelated to arsenal dwarf:
6) Never ever ever put your military in the "Training" alert level. It doesn't work right, and the dwarves get "stuck" and won't do anything. To train your dwarves, remove all their jobs, leave them "inactive" and assign them a training barracks. When they have nothing better to do, they'll go do Individual Combat Training in the barracks. Some dwarves are apparently lazy, and won't ever train in this way, but for 95% of them, this'll work fine.
All that being said, it can take the arsenal dwarf quite a while to hand out all the assignments. When your military starts getting really large, it becomes almost a full time job for him. I think in a tiny fort with 30 or less dwarfs, its probably faster to let the dwarves get their own stuff.