I'm pretty sure the Diana is an Isoly clone. Much of the diana exterior detail is clearly styled on the Isoly, the way the back slides off is exactly the same, the real giveaway is the little locking catch on the bottom. On the diana it's marked open/auf lock/zu... exactly the same as the German Isoly.
Like many Agfas they came in various guises with a variety of lenses, some sharper than others, so you can't grab any isoly if youre going for a certain look.
I'm another closet Agfa fan (various Isolas, Isolettes, Silettes etc) but only one Isoly, with an achromat lens, and I've only used it once so far but I think it deserves more.
[Sorry, image deleted during forum software upgrade. Please re-upload if so inclined.]