Well, politically, it’s basically replacing one main prop for the monarchy with another. The Tyrells would definitely be looking to replace Lannister appointees with their own people. On the other hand, they’re better at PR and making alliances and sharing the wealth, so there’s going to be less resentment.
Personally? Margaery would definitely be a lot better at managing Robert, because she’s better at performing than Cersei ever was. Robert would probably be besotted and over-the-top-generous in that class mid-life-crisis second-marriage way, although he’s probably still going to drink too much and sleep around eventually. Very much likely to do that Henry VIII I’m still young thing – big question there is whether Margaery can get him to whip himself back into shape or whether she’ll have to fake being in love with OldElvis Robert.