I would expect that the AntiDDoS service offers protection at TCP/IP layers 3 & 4 (transport & application layers, respectively). See:
Very few DDoS attacks happen at layers 1 & 2 (network access & internet, respectively) without some kind of device to assist them (rogue/compromised router, etc…esp true for layer 1 attacks).
As for throughput, you'll have to ask Linode support about that. There's also lots of docs about this subject at the Linode marketing site (https://linode.com) and a few posts in this forum as well. Search for them…