Are you Leica LTM users (IIIf/IIIc/etc.) comfortable using your Leica's without an auxillary viewfinder?

I love my M3 and my DR Cron but this combination isn't really THAT compact and so I'm debating on trying a IIIf/IIIc with a collapsible Summicron (or Summitar) or maybe just getting a collapsible and sticking it on my M. My concern with the IIIf/IIIc is that the viewfinder is too poor and sticking an auxiliary viewfinder will be self defeating.

I'm not interested in much anything else.
-IIIg's seem to be bulkier and more expensive than IIIc/IIIf's...I might as well stay with an M
-CL's and most things more modern (e.g. Bessa) seem to not be as durable.
-I don't like most P&S's because I want to be able to focus and I prefer all-mechanical bodies anyways.

I have a Rollei 35 and a Kodak Retina but I can't focus accurately enough with the former and the later isn't that ergonomic.