[Brightcolours]

Good point about the 20-40mm, that lens is a mystery - slow, expensive, soft etc. The appeal is the nice build I guess, but that's where it ends.

 

As far as the 560mm is concerned, it is quite sharp from what I have seen so it is a good lens, just quite overpiced. 

From what I have seen, it is not overly sharp, has so so bokeh and very heavy CA.... 

And then it does not seem to be a real tele lens (rather a long focus lens). Notice the strangely long dimension of 522mm? 

 

Real telelenses are shorter. 

Some examples:

Canon EF 500mm f4 L IS USM: 387mm

Nikkor AF-S 500mm f4 VR: 391mm

 

It seems to be designed by a newbie. Not sharp or contrasty at all wide open (f5.6), weird optical design with a build length of a simple long focus lens, as if telelens design had not happened, and strong CA for a tele prime.

 

The only two plusses I can think of for this particular lens is that it has AF which my Tamron 500mm 8 lacks, and has much nicer bokeh than that lens. For the rest.... better look at the new Tamron 150-600mm f5-6.3 VC USD instead.

The appeal of the other limited lenses is also there I think. They have good (if not exceptional) optics with a unique build and small size that has Leica type charm without the price. Handling your standard plastic lens seems rather dull in comparison. These characteristics may not appeal to everyone though.