It's impossible to know what to make of Meagles. The possibilities are so different that there's not even a happy middle ground to safely hug. Instead, we'll just throw out both options and you can see what sticks to the wall.
Option 1: Meagles is the nicest, sweetest guy ever, who just has one tiny flaw. To back this up, we can list a bunch of excellent qualities – he's compassionate; generous for getting Tattycoram out of an orphanage and into a home; loving; a good businessman who provides well for his family; an honest broker; and a guy who eventually helps Arthur get out of jail and start all over again. His only flaw is his snobbery and social climbing. It's this flaw that eventually makes him agree to Pet's horrible, disastrous marriage – and it's what makes him psyched that so many fancy guests come to the wedding.
Option 2: Meagles's glaring mistreatment of Tattycoram is so wildly off the mark that everything else he does pales in comparison. Miss Wade might be overly paranoid, but it's hard to argue with the way she describes the Meagles-Tattycoram relationship. They gave her a strange, crazy name that marks her socially as an inferior being (like a pet, really). They adopted her – but not really, because she's a servant rather than an actual member of the family. They use her as a kind of symbol of how generous and awesome they are, a sort of status symbol.