Breakdown oars look good when they are stored,,,,,as in all the marketing propaganda. But the truth of the matter is, when you need that spare oar, you need it right now! Not five minutes later, after you've managed to take it out from under the seat and put it together. Meanwhile a couple hundred yards of river have gone by not to mention rocks, root wads, whatever.
Breakdown oars should be assembled at the launch ramp & ready for use before hand. That being the case, why bother with a breakdown oar in the first place? You'll never see break down oars on a white water raft. Oar tethers are cheap insurance.