It's just bug fixes. Guess it is the last iOS update for many older devices that won't be getting 10. Not that 10 is a great improvement by the looks of it, mainly gimmicks and OS tweaks.

It can be jailbroken too

cws82us:

 

It can be jailbroken too

 

Pity its not a fully un-tethered jailbreak, once it is Ill be all over it!

There was demonstration of someone jailbreaking a device running the iOS10 beta too which looks promising, hopefully it will be released shortly after iOS10 goes public.

JayADee: I read it's causing iBook problems. Some people can't seem to get iBooks working again. My hubby had all his iBooks deleted but got them back from the store. I have a lot of saved PDFs from online etc. that I don't want to lose. I use iBooks a lot. Manuals, course material etc. So I'm skipping this one until I am either done with the PDFs or put them someplace else.

To be honest, I read your comment thinking 'user error' but I just went into iBooks and noticed all of my saved PDF's are gone!

or did I just commit 'user error' ..... 

firefuze:

 

To be honest, I read your comment thinking 'user error' but I just went into iBooks and noticed all of my saved PDF's are gone!

 

or did I just commit 'user error' ..... 

 

Please keep us updated on what's going on with iBooks behaviour and this update.... thanks

As usual, YMMV.

For me, my iBooks are displaying and I can read them. Then again, I have a library of  ±10 free books that I only look at when changing phones.

My purchased iBooks and my own saved PDFs are still present, so it doesn't affect everyone. Chances are it's just a vocal minority, but it's still a bit of a risk and it's a hassle to roll back to 9.3.2 (while Apple still offers the signatures).

No problems with ibooks. I suspect it will just be a few under certain conditions. I think the newer sync function across multiple devices is problematic, because I have never been able to get that working properly. But that was introduced some time ago. Apple aren't great with the cloud.

Update is spot on for me on both an iPhone 5 and an iPad Mini 4.