I just received this buckler in the mail last week, after ordering the Marozzo 13" buckler from Therion Arms:
http://therionarms.com/reenact/therionarms_c910.html I am really pleased with the Arms&Armor buckler, as its slightly smaller size makes it easier for me to move through the guards from MS I.33 quickly and it has a deeply domed central boss (its real shape is not very evident from their picture) which can be used to buffet an opponent without a danger of poking them, and it forms an internal ridge which assumedly would easily catch a sword-tip if used as a target.
The Marozzo buckler is larger and of course heavier, and I'm going to have to take my MIG welder to it before I feel comfortable using it for sparring as the edges and corners are sharp. Also, the handle tends to dig into the hand so I'll be wrapping it with leather soon. The wavy shape of it (it's a repro of the one in p.47 of Opera Nova) feels like it would be quite efficient at wrapping and trapping an opponent's sword/sword arm to the chest.
Of course if one only wants to buy _one_ buckler I would recommend the A&A one, but just be sure not to leave it outside when it rains.