^^^^ This.As far as I know, whiskers should not be trimmed at all. They are a sensory organ (same as with cats) and horses use them to feel the ground when eating. Without them they tend to get bumps and scratches on their nose and mouth. I think some federations/competitions have banned the practice (French, I think?).
Unless you have a very good reason, leave them alone. I personally don’t think “pretty” would be a good reason but that’s just my opinion.
I was wondering if I can use scissors to trim the whiskers on the face's of both of my horses, or if I should instead purchase those "horse shave" things. My horses are really laid back, if that helps.
Step away from the whiskers
I wouldn‘t trim the hair inside the ears either— it helps keep the tiny biting flies out of there
I don't believe it's any more reasonable to trim horse's whiskers as you would for a dog or cat - it's not nice.
If I remember correctly FEI even banned whiskers trimming because it's somewhere cruel. You just cut an organ.
Yes, FEI (Fédération Équestre Internationale) has now banned whisker trimming: Ban on trimming horses’ whiskers for international competitions starts today - Horse & Hound.
Since many national equestrian associations follow the same rules, one can expect to see this becoming more widespread. Not everyone agrees with this decision, but to be honest, there are no good reasons to trim whiskers other than appearances. They are there for a reason. Leave them alone.