A few other points:
Remake is a two card trasher that costs 4. It works quite well with B if you have good 4s and strong fives as you can either remake the B into a 5 & remake a silver into a B or trash estates & coppers.
B is also a strong in settings with good high end trash for benefit cards as it adds 3 coins of value to the deck. I'll sometimes add B to a mid game 4 deck (i.e. after getting the forge, but before I've stopped have 4 coin hands) as it can provide a steady stream of silvers to forge into golds, engine components, or provinces. Likewise upgrading to an engine likes a B opening as the upgrades can later turn the B into a 5 component or keep turning silvers into 4 coin components. Apprentice + B is also decent as you can trash the silvers for draw, regain them with B and save your buy for apprentice/gold/province. A lot of the high end trash for benefit boards hurt for a way to add value quickly and B does exactly that.
One final near unique thing about B is that is a potentially unlimited discard attack. Repetitive plays of most discard attacks don't hurt the opponent, particularly in the late game where you have enough variance to either keep the coin for a province or the needed engine components. B on the other stacks for as long as they have green in hand. If you can attack with B 5 times reliably and the opponent has a sufficient clutch of green in their deck, you can pin them for the rest of the game with 0 card hands. Unlike the KC/masq pins, this one is a lot harder to pull off as you need a lot of green in the opponent's deck, you need to have a way to reliably deal with the silver accumulation, and you need to have the opponent lack a way to cycle past the green with one or two cards until you can fully pin them. A setup that works, though rarely without a weak opponent or good reason to acquire alternate VP cards, is apprentice/TR/B which allows you to chain TR/apprentice for +actions and play B several times. The apprentices can also trash silvers for draw to get you some combination of TR/B that lets you push back 5 cards. Other options include using watchtower to trash the silver, upgrades to turn silvers into TR or some other engine card, and less generally with other strong trashers like forge & governor. Oddly enough, loan can actually be useful here to clear out some dead silver to keep the pin reliable.
Take, for instance a 3 player game with 2 players going B/gardens. You can go B/apprentice/TR and set up an engine that can reliably attack with B 5 times per hand. Because your opponents lack draw and you will attack 5 times, they will never clear the top of their decks and eventually they will draw a hand of 5 green that has them facing the choice buy a copper or buy a curse for the rest of the game.
At present, the B pins are pretty shoddy. They take a good number of cards to setup, have trouble being both reliable & point gaining, and often need draw that makes it very hard to lock in the pin. However, as expansions keep coming out, we keeping seeing more cards that can help set this up (apprentice, watchtower, spice merchant, etc.) and more alternate VP that can get green card densities high enough make this work (Great Hall, Nobles, Harems, Farmland, Fairgrounds, and Silk Roads). So this is definitely something to keep in mind for the future.