What flickering do you have? I don't see any. As for startup time, I dunno, seems to open in less than half a second for me, though on a relatively high end laptop. On a 10 year old machine it might suffer.

I rarely use Windows these days, but IrfanView feels lightning fast compared to the built-in Photos app or whatever they call it. I started using IV I think on Win 98 and it's still as snappy and reliable as it always has been.

I haven't used the latest Windows viewer because I'm no longer prepared to upgrade to the latest versions of Windows, but the old version was a dog of a program compared to IrfanView, it was slow, couldn't display many formats and would misbehave if the image files were damaged.

And yes, at times it flickers and or images can tear.

The recent photo viewer is great. I never felt the need to install Irfan anymore just to view photos since .. a long time now.

I mean why would I? If all I need is viewing a couple of photos every now and then, cropping and rotating one or two and drawing some circles on them to highlight something in a screenshot and Windows already does that then why bother with Irfan other than habit and nostalgia.