No, no, no, no and NO
Both bucklers are horribly unrealistic (in the OP way) in this game. You can block arrows even though you really shouldn't, and the round one has like double the effective coverage of any rectangular shield, just because it's round. Also, they both look terrible.
The same applies to all shields. A reality check is much needed when you look at what round and non-round shield actually cover ingame.