I absolutely adore my mamiya 6es. Superb lenses, a light and fairly compact body that has a rather low profile, handles very much like a 35mm camera but provides far more detail. The body collapses down to almost nothing- I can easily fit two bodies and all the lenses into one little shoulder bag... or just tuck one camera and lens into a jacket pocket.
My usual caution to those interested in a the 6/7/7ii is that the lenses aren't fast, so you can't think of this camera as an available light weapon like you might think of some 35mm rangefinders. The VF, though, is big and bright and wonderful. And scale focusing is very simple and straightforward. Stability wise, I routinely handhold the 6es down to 1/15 and beyond, no problem. The MF RFs are not as versatile as a MF SLR, nor should they be; but they are weapons for scenic and landscape photography and such, and they are fabulous for travel. One mamiya 6 plus three lenses easily goes into a little bag. I am looking at the bag I just used now, it is 6" deep, 6" wide, and 4" deep. So... pretty small.
Mind you, it's just not right to even compare a 6/7/7ii to a hassie or any slr for that matter, it's a totally different tool. You have to find out for yourself if it's right for you. Try it. Give it a real chance. Changing gear, in a fairly radical way, can be a great way to re-energize your photography and find new ways of looking at subjects. RFs in particular force you to imagine the DOF and imagine the 2D rendering whilst looking at the subject in 3D. Some people never become comfortable with that, for me it was way more natural than looking through an slr VF. Go figure! Everybody's different. I find the 6 extremely easy to focus, on all the lenses.
Winder... I don't know about the fragility of the winder, I am pretty rough with my gear and so far no issues. I bought a "bgn" grade mamiya 6 from KEH as a backup and I use it routinely now.
If you are in doubt, then consider picking up a fixed lens 645 Fuji RF. For $500 or less you can get something super portable and nice. I used to have two Fuji 645 RFs and loved them. I did trade them in when I bought into the Mamiya 6 line, and I don't regret that at all, but I am definitely not going to knock the Fujis.
P.S. I find that changing film on the Mamiya RFs is simple and fast, as is changing lenses. I mean I am pretty sure I could comfortably do both in the dark in about 5-10 seconds. In fact, I know I can because I used to shoot lots of IR with the 6es and changed the film in a changing bag. Whatever you shoot, you need to become so familiar with it that it fits like a glove. Life's too short to fight your gear- if it's not comfortable for you then ditch it and move on.
P.P.S. I suppose it's worthwhile to mention that of all my cameras, the 6es are the only ones with a resale value that has gone up rather than down. If you absolutely must, I'd not be afraid to trade in your other camera to try out a 6 or 7 or 7ii for a while... the prices aren't going anywhere. If you lose any money on the deal it won't be much. But as everyone is saying, hold on to what is already working for you... if it is already working for you.
