Every Leica LTM Viewfinder with the exemption of the II /III g,which are very expensive, is of no great value compared to a M viewfinder. It has no parallax correction, the looking window is really very tiny and cannot be used with glasses. You have no RF in the viewfinder and have to look into a separate very window. The base length of the RF is smaller than that of a M, therefore it is not so exact. The universal viewfinders are in fact wide angle viewfinders with variable masks fot the longer focal lengths, they give a left-right interchanged picture. The screw Leica is much louder and has more vibration than a M. The loading is even more tricky as you have to cut the beginning of the film to the old Leica form and the body has no opening door. With a III c you have no flash sync, with the III f you have to use special contact numbers with 1/25 or 1/30 sec or longer. Many old screw Leicas have problems with varying and sometimes lacking spaces between the negatives. The separate accessory viewfinders for only one focal length are much better, but with each lens change you also have to change the viewfinder and sometimes you will loose one (some 100 - 150 $).