The Corellian/B-wing was essentially flying junk, typically only used by cash-strapped pirates, built using wreckage found at various battle-sites.
The Ugly's mission profile usually only required the vessel to damage lightly shielded targets. Against heavier-shielded and better-armed vessels, the Ugly was less than a match. The cobbled-together nature of their construction also meant that very few Uglies could be relied upon to perform at anywhere near peak levels.
A large number of these Uglies were employed by the Sacorrian Triad during the First Corellian Insurrection, but they were no match for the Bakuran fleet's General Purpose Attack Fighters.
Later "refinements" to the design included an anti-infantry turbolaser, intended for use on the ground, attached to the ship's undercarriage.