Id pass if I were you. This item is not solid, all. Pieces are flimsy and frail and this means if its windy, the entire pergola will shift and rock, even if properly fastened and secured. The hollow posts mixed with any adverse weather results in the fastening screws loosening, which in turn, leads to additional swaying if the wind blows. 

My suggestion is to spend the 600 that this poorly constructed pergola costs, and purchase lumber materials to build a proper pergola. Save yourself and your wallet the heartache...skip the purchase.