I have a Leica IIIa with an Elmar 5cm and I think it's a great user to keep in your pocket. With the lens collapsed it's tiny. How user friendly they are though depends A LOT upon your own experience. If you're used to shooting LF or antique cameras then you should have no issues. However, if you're used to shooting fully auto cameras or modern SLR's where all your shot info (shutter speed, aperture, metering, etc) is in the VF, then it may not be your cup of tea. 2F/2F makes a good point about judging exposure. I take a general exposure reading and then make adjustments based upon experience for when the lighting varies. As for loading film, I don't find the actual loading part to be an issue at all. It takes only a couple of seconds longer than loading my OM. The PITA part is remembering to keep rolls with trimmed leaders in your camera bag.
"A good photograph is one that makes the viewer so aware of the subject that they are unaware of the print."- Kodak
"...if you find afterwards that you made a mistake, the price of the film and chemicals was...tuition!"
"The hard part isnít the decisive moment or anything like that Ė itís getting the film on the reel!"
- John Szarkowski