I ride a Tern Verge D9 and love it. It's comfortable, light, fast rolling and very well built. The fold isn't bad either, admittedly not as good as the Brompton fold.
Reports of the Brompton G Line is that it's not a great ride and heavy but looking at the specs for the S8i, they do weigh similar.
The S8i comes with a Gates belt drive, internal gear hub. Those two things alone would swing it in my favour.
I have a commuting buddy who has a gates belt drive on his bike and he's only ever had to change it once in 10 years. So it really is fit and forget.
I was soured by Brompton as when I did have one, it fell apart, it really didn't stand up to a tough riding daily commute in all weathers even though I am a stickler for looking after bikes and I found the 16" wheels an uncomfortable ride. So sold it on and turned to Tern and it's something I have never regretted, chalk and cheese comes to mind with the riding that I do.
You do have Brompton fans who will say Brompton and nothing else and that's fair and looking at your forum handle you know your Bromptons anyway.