I have one and like it. But mine is a tight squeeze for an M body and non collapsible lens, however an LTM body with a collapsible should be perfectly fine. (The problem being the depth of the of the body with lens as much as anything and getting it in and out without coming in too harsh contact with the zipper is the issue). I think they are now made in different sizes so the larger one should be even better if you want to carry a small spare lens like the 90mm Elmar. Like all Billingham gear they are extremely well made, nice looking and long wearing.
The way I prefer to use mine is the Leica M around my neck and a couple of M lenses, cleaning tissue, spare memory card ( if shooting digital) etc in the bag.
Or if I travel overseas its ideal to carry my passport, wallet and tissues while on the plane and my camera etc is on a large Billingham. Hell it IS a man bag!!!!