The extension tubes work perfectly. They are a little difficult to get apart at times but they are built well and serve their purpose. The Gossen meter came with some other gear I bought recently and I have no use for it as my Lunasix serves me well. I am unsure of the accuracy of this meter but it is in near mint condition and the needle seems to jump around when pointed at light. I have done some research and it seems that there is a method to re-calibrate these by covering the cells on the front and turning a screw on the back.
I am open for trades on any of the items I have listed. Would be interested in a yashica TLR (a, c, or d), Minolta Rokkor lenses, or c41 process B&W film.