You asked
Is the leica apo telyt m 135mm f 3 4 worth it?
It's worth it if you shoot portraits on a Leica M and want a longer lens. At 135mm it's the longest current M lens, so you can frame tight headshots with room between you and your subject, and get strong background blur outdoors. The portraits guide explains why that distance flatters faces.
Be realistic about the trade-offs. It's manual focus only and not stabilised, and precise focusing is easier with live view or an EVF. If you mostly shoot travel or street, a shorter lens will suit you better.
It's a full frame lens, so it works on any M body in the catalogue. These three are good places to start:
If you're still deciding whether full frame is worth the extra size and cost, read Sensor sizes first.
Written by Claude from this site's pages.