Hi everybody.
Quite hot discussion here now, so let me explain couple things myself.
V2 adapter tweak referring to is discontinued. It was made by personal order once when I thought Redstan is out of business, but it seems that I was wrong. So, we will not continue to make such adapters with retaining ring (that is really great idea, and it is sad that it wasn't mine :-) )
Our adapters are more simple and more risky. bzpop is correct - there is a chance of dropping anamorphic attachment with our adapters, so you need much more care using them. Positive side is lower price for those who using not too expensive equipment.
Flat spring bzpop referring to is not poor design. Purpose of the spring is protection of the lens body from damage by adapter screws. I tested this feature on many attachments already, and results are following: if you tight the screws just by you fingers, an attachment will not fall accidentally, but can be pulled out with not too much force. After you positioned it correctly, you need to tight screws bit harder using allen key. After this, you'll not be able to pull it out. So, this design is secure enough when used properly.
Thanks.
Raf.