He left Francis I in order to serve Cosimo and never ceased to regret the change.

The Perseus was his greatest accomplishment for Cosimo, and the narrative of its casting is terrific and not a little like Dumas.

When it was uncovered in its present position all Florence flocked to the Loggia to praise it; the poets placed commendatory sonnets on the pillars, and the sculptor peacocked up and down in an ecstasy of triumph.

Then, however, his troubles once more began, for Cosimo had the craft to force Cellini to name the price, and we see Cellini in an agony between desire for enough and fear lest if he named enough he would offend his patron.
The whole book is a comedy of vanity and jealousy and Florentine vigour, with Courts as a background.

It is good to read it; it is good, having read it, to study once again the unfevered resolute features of Donatello's S.George.Cellini himself we may see among the statues under the Uffizi and again in the place of honour (as a goldsmith) in the centre of the Ponte Vecchio.