I have a 139Q. I think it is the lightest and smallest model of the line. It is only slighter higher than my Pentax MX which is famous for being small as an SLR, but it is shorter than the MX. It feels rather sturdy in hand, and I find it easier to hold than the MX.
I like the black finish of it. The viewfinder is not the largest, but then eye point is higher than the classic metal manual SLRs from the 70s. I wear eye-glass so I actually like it more than the wide and grand finders on Pentax MX or Olympus OM-1.
The Copal(?) shutter equipped on it is more carefree than traditional cloth shutters. But the noise and shake is bigger.
The lenses for C/Y systems are more expensive than P-K here in my region, even the Yashica ones. I think it is the same on eBay.
It is a camera that I would keep. If I'm travelling with it, I would buy a manual model only Yashica body as backup, since the electronic 139Q are more prone to failure.