My experience was like

I use once, first time few weeks ago & I never went back to using E-Gates for passport scanning. My passport is now always in a zip lock bag in my pocket
Only problem with MyNIISe at BSI (I've no experience at KSAB) is difficult to login due to poor internet coverage (no WiFi provided) - need to login to generate the QR Code.
To overcome this I'll do screenshot of the QR Code before I leave home - QR will expire in 6 hours after generation.
But sometimes MY's Immigration Officer says the screenshot of the QR isn't "legible", if this happens (never experienced this before) then I'll login in Offline Mode & generate another QR.
However nothing is perfect as Offline Mode sometimes cannot generate QR Code - don't know why & I've not experienced this before at the Immigration Counters (only at home I see this issue).
MY currently has 2 QR Code apps for Immigration Clearance: MyNIISe & MyBorderPass.
MyNIISe will finally be adopted officially. I suspect the latter will be dropped very soon - Foreigners cannot use the latter too
The strange behavior among (bus paxs) users of QR Code is they prefer MyBorderPass. I think near 100% of QR Code users use MyBorderPass while like no one uses MyNIISe.
At the Immigration Hall each app has their own Counters (for MyNIISe at BSI Counters 9 & 10, KSAB Counters 8 & 9 - for both Entry & Exit), so you can see MyNIISe like no one is using. The 4 designated Counters are specially assigned from the same ones for passport stamping but with a red light scanner atop the Counters, not specially made Counters.
I think 99.99% of SG taking bus don't use MyNIISe, most are still using E-Gates with their passports.
SG QR Code users are mostly bikers or cars.