New to the forum and having a bit of a brain block trying to work out which Q/R clamp I'd need for my 5D?

Both clamps look similar in the pics but 360 Tactical in the UK only list the non Arca one on their site.

Also there's no centre mark on the L bracket but am I right in saying that that shouldn't be an issue as we're only concerned with fore and aft movement?

Thanks