While barbwire is of course in no way ideal for horses, there are a lot of things to think about.
If the paddocks are big, and the fences are maintained as shown in the pics I would not have any hesitation in putting my horses out there.
I agree that a stand off hot wire on the insulators would be a great idea, teaches good respect of the fence.
I have been around horses for 40 + years now, and I think that every single place that I have been involved with had barbwire fences. At present I only have either straight barb, or barb over the wire square stuff, there is no way I could afford to rip out several miles of fence and change it.
I would choose lots of things over barb, but at the same time I would choose a well erected, properly maintained barb fence over a lot of other things.