Looks like you and couple of chaps can tell the difference.
I personally fell into the trap of stereotyping automation with speed. After a couple of trips, I sensed that manual was faster. I called up a chap in ICA and complained that manual was faster. He told me that nowhere did ICA claim that it was faster. And he was right. ICA was spinning media releases using "express","convenience" and "on your own time" but never say faster.
He explained that enhanced Immigration Automated Clearance System (eIACS) had one additional security feature that is fingerprinting screening which manual does not have.(though using wrong passports by accidents or for illegal reasons). Just like all Chinese look the same to AngMo, I suppose immigration staff are challenged when looking at foreign photos on passports since we have foreigners who are residents in Singapore. He also said that it is save staff costs.
After that explanation, I did notice that when both both the automated and manual lanes were clear, and new arrivals came in, the manual one cleared first. The automated one had 2 stages, passport scanning first, gate opens, then fingerprint scanning, so natuarally longer compared to passport scanning only at manual.
I have since found that there are no plans to increase automated lanes as too many complaints about speed and issues with too wet or too dry fingerprints.
I suppose the only good use is when one wants to avoid bad customer service when facing disgruntled ICA staff that can spoil your trip.
Manual clearing is faster. Automated only appear faster because the line is short. If there are a few blur sotongs in front of you, automated is very slow and frustrating.