In my youth, I could inflate a 14' raft with a 4" barrel pump as fast as a metro pump could do it. Now I just use the metro until it whines a little, then top it off with the K-Pump. Same amount of time with quite a bit less work. I can still win the race to inflate one chamber.
The double action wonder pump is worthless as far as raft inflation goes, but they are perfect for IK's and SUPs and they are kid friendly. I have found them most useful for deflating paco pads in the times I roll them up and wish to reduce their bulk. They also can stoke a pile of coals to make them ready to cook on in 10 minutes. (don't melt the nozzle!)
The 5" barrel pump would make for about the same amount of work on a 16' raft as the 4" on a 14' raft.
So like everything, there is the right tool for every job.