I'll give you my philosophy as I go through the same selection right now and will be doing the testing and selecting early next year. I'm matching the optic to both how I intend on utilizing the rifle and how it will perform.
My chosen optics are as follows with full package pricing as I paid for them: NF 2.5-10x24 Mil-R in an ADM Delta mount and angle mounted DeltaPoint ($2000 but rare), M-TMR CQBSS in straight rings (I paid more on mil discount three years ago than found new now, available used around $2100), Vortex Razor II 1-6x JM1 in ADM Recon-X (great demo deal I got at $1250), and EOTech EXPS 3-0 ($500 after recent rebate). Save round for a Leupold Mark 6 1-6x currently on a different rifle, but might give it a whirl since it has the CMR-W 7.62 reticle in it.
My objective is a lightweight, heavy hitting compact rifle for sport shooting and hunting in the east. Got all the glass, mags and Geissele trigger, waiting to drop the hammer on the rifle in a few weeks so it doesn't take up space in my dealers safe while I'm still overseas. I've played with them, liked it, can't wait to get one of my own and really wring it out.
I see the SCAR 17s for what it is - a lightweight 7.62 "battle rifle" carbine that while capable of putting up decent groups, really belongs in the hands of someone with restless feet and itchy fingers rather than riding a bench. I'm trying to see how light I can keep it in comparison to my 16" large frame .308 while putting them head to head in performance. If it isn't as accurate in my hands as the others but runs like a raped ape, it will probably keep the EOTech on top and live on a diet of 147gr ball ammo. If it's dropping rounds exactly where I'm intending on putting them, then the NF it is. If it shits the bed, well it will be posted on Gunbroker next scare and I'll pocket the profit. A case of Federal ball and a case of BH 175s are waiting on me for some fun. Don't worry guys, I'll be documenting and posting the results up.
What I would recommend to your buddy is to first decide how he wants to use it (bench or shoot and move), see how it will perform in all out accuracy hopefully using a scope borrowed from another platform, then select an optic that will match that combination.