I trialled a medium screen on the 650 but this directed wind to my forehead - it was fine downwind but a pita into a headwind or side wind. Removed it.
I’ve done 10,000k without a screen and don’t miss it at all.
If the Himi screen works, fine. If not, I’ll remove it without a second thought.
None of my bikes have had screens and that’s going back to late seventies.
I went without a screen and it was wonderful, just the wind rushing past my helmet, but it does leave the back of the instruments exposed so I got a super shorty to protect them.
If you have any plans to fit a GPS, you may want one higher to protect that.
Also, if you fit Barkbusters, you'll need to move the stock screen into the forward position. I'd recommend the Barkbusters just to protect you in a fall or with trees whipping past. The stock bars are made of congealed pasta and bend really easily but I wouldn't change them until you fall off and have to.
I bought a second handle bar clamp (via ebay, stock RE part) and have placed that under my bars. This effectively gives me 20mm risers (and look good as opposed to some aftermarket items) which makes it more comfortable for me to stand. Mind you, I'm a six footer. However, it allows me to run the screen in the rearward setting with Barkbusters fitted and that, I think, is a plus.