I have successfully cum on all of my gfs' faces with varying degrees of success.
DISCALIMER: I am absolutely obsessed by facials, so I might be biased.
Generally it gets easier with time. Don't try to do it on your first night or you might get the reactions you read in some other posts.
Even if some girls don't love it, if they are horny they will get along with it. Women generally tend to accommodate men's requests, it's part of their sexuality.
Their receiving nature, bot of dick and semen, makes it easier. Plus, sex is a show and going along with the flow is crucial.
Imagine stopping the act for any small unpleasantness one might encounter (hairs in mouth, too close for the smell, too much force or too less, and so on)
Generally, I never say it upfront the first time, I try to sneak it in the heat of the moment, like reaching an insanely hot climax in which she loses her mind.
You understand that this cannot be done every time, so if you imagine your gf more like a cum dumpster, you need to get really lucky and actually find girls who get turned on being sprayed in the face.
Reactions are mixed. Most just take it. Some enjoy it and add their touch, like cleaning their lips with their fingers, or eating small pieces to make you horny.
Others just go into apnea, contract and wait for the worst. I usually congratulate this type of girl for being brave and horny.
So, it varies a lot, but at the end of the day it's really nothing big. it's like the most natural stuff (have you seen dogs peeing to delimit the perimeter?)
From a man perspective, it's perfectly natural to want to mark your prey after a successful hunt, we have this built in, otherwise we wouldn't get excited about it, nor girls would allow it.
Now the last part: what do you do if they don't take it in the face?
I got pretty lucky so far, so I have been able to finish off always in their mouth, unless I want to spray it all over their bodies.
Once in their mouth, I can safely say that 90% of the time they will spit it out, but a 10% they will swallow it, even if you don't ask anything.
My first gf would always swallow it, I don't know I think she found it more efficient, instead of going to the bathroom and spit it out. My last one would drink it 1 out of 20 times.
Also at this point, one cool thing you can do to get them used to your jizz is to make them suck your dick clean after you came in their mouth/on their bodies. This might make things easier with facials down the road.
So I hope you found this useful, I believe facials are a way of life, and I look forward to spray my shit on more and more girls in my life.