Be it this ad network or any other, you will find ads slowing down the website. In fact, due to poorly optimized campaigns on Adsense, i find that adsense actually slows down the site considerably. However, adsense is of google so google probably keeps a filter separately for adsense. Nonetheless, to balance the loss of speed due to ads, you need to make your website very fast and probably invest in CDN’s, cache plugins etc. Optimize them as much as possible so that your site loads very fast. Then a delay in ads loading will not affect much.