Not entirely sure about that spelling, but it might just be a Welsh variation. It’s also an Irish name, but in [name_f]Ireland[/name_f] it’s spelled [name_u]Fionn[/name_u]. It’s pronounced as you wrote, although the emphasis lies on the o sound, the ‘ee’ sound is said really short in Irish, making it sound a bit more like ‘Fjon’.
I love the sound of the name but when I first saw the name I was not sure how to pronounce it, especially with the two Fs. I agree with you, it’s easier to pronounce than [name_f]Niamh[/name_f] and [name_f]Caoimhe[/name_f].