Among all of the Great Merchants, de' Bardi is one of the less impactful ones. While both of his bonuses provide useful things, his ability pales when compared to such mighty Great Merchants as Marco Polo or Irene of Athens, both of whom are available in the same era as de' Bardi. Most of the time you care about the Gold more than the Envoy. A lump sum of Gold can be used strategically to upgrade units for a timing push, but 1 Envoy hardly changes anything in the city-state diplomatic game. In the Monopolies and Corporations game mode, Corporations are unlocked a lot later, so you can consider picking and saving him just for the sole purpose of establishing a Corporation, especially when the ones you want have gone. Otherwise, save your Great Merchant points for one of the aforementioned ones, both of whom are much superior to de' Bardi.
The most powerful banking and trading company during the Renaissance, the Florence-based 'Compagnia dei Bardi' under the guidance of its patriarch Piero di’ Bardi (named after the family’s founder) would establish branches in England, France, Spain, and elsewhere. It was the money lender to kings (and hence, a “kingmaker”). Even in its declining years in the 14th Century, it would play a notable role in financing early voyages to the New World, including those of Christopher Columbus and of John Cabot.
The doings of the di’ Bardi have been documented since 1164 AD, when Emperor Barbarossa gave the county of Vernio to Count Alberto. Countess Margherita, last of the decrepit Alberto’s line, sold Vernio to her son-in-law, Piero di Luca di Maso Bardi. By 1338, under Piero the di’ Bardi had established banks in Barcelona, Seville, Majorca, Paris, Nice, Avignon, Marseilles, Constantinople, Rhodes, Cyprus, Jerusalem, and even in chilly London and Bruges. The Bardi provided merchants with “bills of exchange,” essentially checks whereby a debtor in one city could pay a creditor in another. Without this sort of portable cash, trade would have been severely hampered.
Piero and his brood also served as moneylenders to the powerful but poor. And this lucrative practice (the interest on loans to kings was high) eventually brought the 'Compagnia' to its knees. During the Hundred Years' War in the early 1340s Edward III of England borrowed 900 thousand gold florins (the most stable and valued hard currency of the day) from the Bardi. And Edward promptly defaulted on these loans in 1345, bringing it to declare bankruptcy and so leaving the trading economy of the Mediterranean and most of Europe shattered (until the rise of the de Medici and Pazzi banking firms a century later).