Edit:
"Repairs seem to be expensive and frequent. My P45+ works well, this far, but some good posters on these threads have indicated that backs can be quite problematic. To be more specific, one of the posters I trust pretty much had repairs on all backs he had. Send me a PM if you need a reference.
That's absolutely untrue. The median number of service calls (calibration, repair, maintenance) for a back we sell is zero.
The poster you're referring to had several *calibrations* done not several "repairs". He's especially picky (well within his rights with expensive gear!) and had especially bad luck - a bad combo."
I may be the poster referred to as picky, and I actually don't feel I was being too picky (if it was me), considering that the IQ260 came back to me in a condition that rendered it non-useable in any type of normal light, i.e totally blown highlights. And considering that the back had gone in for a "repair" -- "replacement" of the WiFi top plate, in perfect working order and came back to me in that condition was a bit of a shock. The greater shock I had was attempting to get Phase One to agree that there was a problem as once they found out I was using a tech camera, they tried to blame the condition on the tech lens, even though I had many thousands of previous frames with same back and lens, and none showed the issue. I was lucky enough to still have my old DF and showed Phase One that the same problem was occurring with that combination, then they were able to allow a return.
Back to the OP's question.
The DF and DF+ are well build camera bodies, based on the older Mamiya 645 series. They are heavy, solid, and all the control surfaces are well laid out. The main difference between the DF and DF+ is a vastly both more accurate and faster locking AF system. arThe DF+ also ships with the Li-on battery back, which is also much better than the 6 back AA back that the DF takes. You can purchase the Li-on back for the DF and if you plan on using a DF a lot I would make the purchase. AA's Alkaline have a linear drain and are not well suited to the DF body. Li-on AA work much better but are much more expensive. You still only have 3 AF points and really as the outer 2 are so close to the center, you in effect only have 1. Both bodies have to have firmware upgrades done with the V grip installed. If you own a V grip you can do it, if not the the body has to go to a dealer for the upgrade. Finder on the DF, or DF+ is bright, but I never found it bright enough for very accurate manual focus, especially with wides. Telephoto lenses are much easier. There is a magnifier that can be added to the viewfinder that makes detailed focus easier. If you pick a back with USB3, you can also tether to a Surface Pro or similar device and get excellent focus feedback on the fly and in the field.
Net, the DF is not a DSLR body, no way to compare it, feature function, connectivity etc. The back and DF really are two separate entities. This has gotten a bit better with the DF+ and IQ backs, but still it has a long way to go.
Lenses, you have huge options.
You can use older Mamiya MF glass, some of which is very good, you can use Mamiya AF lenses or Phase D (Digital) lenses or the Phase One LS lenses (leaf shutter). Most of the wides are OK, 28mm, 35mm, and 45mm, but other lenses are excellent, 55mm (AF), 75-150, 210 AF, 240AF, 55 LS, 110LS 300mm, to name a few. Many of these lenses will show up on the used market but new, they are priced in line with Pentax 645z lenses (new design).
Some of the older Mamiya MF lenses, 35mm, 45mm, 150mm are very reasonable used and have very good optics.
If possible, I would seek out a dealer and try to demo the DF or DF+ with a few of the lenses, in the focal range you are looking for.
Paul
