Is the Phase One back a good value? If so which model?
So .. Hasselblad V - that will cost more than Hasselblad H, almost 2x for the same back.
Again, what is your $? It's a hard question to answer - but under $5K? $10K? More, depending on the features?
When I started in on digital backs (Hasselblad V), I use the <$5K, and must be able to run untethered. I started with a P30, which died early. But that taught me two things, a) I wanted a larger sensor, at least 2x FF, and b) I wanted another digital back. I ended up with a P25. It was slow and clunky, but worked. Despite what people have said about how slow and hard to see these devices are (compared to current Mirrorless), now you could view, magnify and check both focus and exposure before packing up and hiking out of the grand canyon - unlike when using film. When servicing cameras, now it took a few hours to adjust the focusing screen, where as with film, it took a few days (you can see the back-focus on a 2/110 Planar just as easy on film as on digital, it just took way longer). The main issue I had with the digital back was managing batteries on a 2 week wilderness trip. And the fact that it was smaller than 6x6. Of course you could just use film then.
In the lower cost end (for >2x FF), you have P25, P45 from Phase, CF39 from Hasselblad. I'm less familiar with Leaf, but they are similar models. When you go higher, you get P65, and IQ's up ~v3 form Phase, and CFV backs from Hasselblad. If I shot more professionally, I would get the last Phase back with the 52x40mm ccd sensor that came in V mount.
Batteries are not an issue, they all use the common easily available Canon or Sony video batteries.
CF card are still easily available, and you do not need a huge card, you cannot shoot that fast!
The common issues with the older backs are the hot mirror (IR cover glass) corroding (it develops spots), which is easily seen, and not hard to repair. Hot mirrors are prone to this, especially early ones.