I did think you dropped the ‘e’ in [name_u]Hayden[/name_u] before I thought ‘oh, like the composer’. 
That makes me like it much more if it makes any difference! I think it would age fine. But I do think it will be confused a lot with [name_u]Hayden[/name_u]. I suppose it’s easy enough to say “hye-den, like the composer” but that might be annoying/get old.
The only [name_u]Haydn[/name_u] I’ve ever met was a girl, and she pronounced it the same as [name_u]Hayden[/name_u], so I think it would definitely be mispronounced frequently. I don’t like Hyden or Hiden, but I do like [name_m]Hyde[/name_m].
I think almost everyone would pronounce it [name_u]Hayden[/name_u]. It looks like [name_u]Hayden[/name_u], but misspelled.
It will be pronounced Hay-den. I know a [name_u]Haydn[/name_u] who is in his mid-twenties, and even he pronounces his name hay-den. You could just correct people, but you and your child will do it all his life.
I think it would be a touch unfair to your child to give him a first name that will be mispronounced AND misspelled 99% of the time.
If you do want to use it. Though, I’d figure its fine in the middle spot. People will still not know it, but that’ll come up soooo much less frequently
I personally love this and immediately linked it to the composer. It was on my name radar. Yes people will mispronounce and misspell it, which is a shame, though easy enough to correct. My nephew has a name like this, though one step further in that it has no automatic reference for even a minority of people. He is five and has no problem correcting people in both the spelling and pronunciation of his name. I think it’s a matter of how you deal with those obstacles that will help determine how “annoying” this will be for your child.
It’s a great name, great historical reference. If you love it, go for it. If you’re on the fence or think that it would be upsetting or irritating for you to correct people then leave it.
I immediately connectted it to the composer, and although I know most won’t, I still think it is a lovely name. I honestly prefer it to [name_u]Hayden[/name_u]. Yes people are going to mispronounce it but once they are told once or twice it shouldn’t be an issue. There are names in the world that are more confusing than [name_u]Haydn[/name_u]. And please please please don’t change the spelling, I think it would lose the musical sofisticatedness that [name_u]Haydn[/name_u] has, and it just looks strange…