I just fall in love with the name (both spellings) and I’m wondering what would you think of it? Is it usable? Too trendy? What image do you get from it?
And just being curious, would it be okay if used on girls?
Makes me think of [name]Prince[/name] [name]Rainier[/name], which isn’t necessary a bad thing! Is it usable, yes. Trendy, not at all - i’ve never heard of anyone with this name except for the aforementioned [name]Prince[/name]. Can it be used on girls, imo no - it’s a solely masculine name.
A mountain and a prince – very handsome. Not trendy, but I wouldn’t use it on a girl.
I like it; but have very little experience with it as a name. I don’t think it can really work for girl, the alternative would be [name]Raina[/name]/[name]Reyna[/name], almost identical sound with an established female usage. Best wishes! 
I really like [name]Rainer[/name]. It’s an undiscovered gem with a string, regal sound – but only for a boy. I think of [name]Rainer[/name] [name]Maria[/name] Rilke.
I love [name]Rainier[/name] but not crazy about [name]Rainer[/name]
What pronunciation are you going for? To me, [name_m]Rainer[/name_m] = “[name_u]Rain[/name_u]-er” (as in, one who rains), [name_m]Rainier[/name_m] = “[name_u]Ray[/name_u]-near” or “[name_u]Rain[/name_u]-ear” (like [name_m]Prince[/name_m] [name_m]Rainier[/name_m] or Mount [name_m]Rainier[/name_m]) and [name_m]Reiner[/name_m] = “rhine-er” (like the producer [name_m]Rob[/name_m] [name_m]Reiner[/name_m]). I think that [name_m]Rainier[/name_m] is the clear winner. (all of them only for a boy)
I know a little boy named [name_m]Rainier[/name_m]. I think it’s an awesome name, but definitely all boy to me, perhaps because I know a boy with it. Very strong, handsome name.
I really like [name_m]Rainer[/name_m]! It’s all boy to me, though. I think of the brothers [name_m]Rainer[/name_m] and [name_m]Atticus[/name_m] that have appeared multiple times on [name_f]Ellen[/name_f] Degeneres’ show…they are experts on U.S. presidents. I don’t think it is trendy at all!
I like it, but I’m loving [name_u]Roan[/name_u]. [name_m]Just[/name_m] saw it on some child model…but I like it anyway.
Sorry but I don’t like it at all. The French pronunciation of Renoir is alright but otherwise is too much R and just doesn’t sound good and is sort of a mouth-twister. I definitely wouldn’t like it on a girl because I strongly dislike the whole “boys names on girls” trend.
I like [name_f]Rayna[/name_f] for a girl, or [name_m]Rainier[/name_m] for a boy. I don’t like [name_m]Rainer[/name_m] at all.