As always on this forum, an interesting thread......
My tuppence worth.....
I believe that the open/closed debate was more relevant in the earlier days of digital. People were gradually migrating from MF film to MFDB and, understandably, wanted both choice and flexibility, without having to break the bank. If possible, they wanted to adapt their existing MF film system to digital. Phase have continued to offer this more than just about any other back maker.
I had been using (and still very occasionally do) Mamiya RB67s for over 20 years. They had paid for themselves many times over and, as Ebay will testify, are worth very little. I could buy a back for them, or I could make a clean break. I chose the latter.
As luck would have it, my timing has been perfect. By upgrading through Canon 40D, 20D, 5D and now IDsMk3, in parallel with shooting 4x5, I have managed to hold off on the purchase of MFDB until this year.
In January, I availed on Hassie's offer of €6k off a H3Dll 39Mp MS. I got it with a 50-110mm, 80mm, spare batter grip and second grid screen. To avail of the offer, you had to trade in any digital camera and a lens. I went out and bought an old Canon lens for €40 and gave them my 40D with it! I *always* haggle and if I told you what that entire package cost, it would make you weep. It was NOT list. I promise you!
In addition, during the four months I was waiting for the camera to arrive, I had unlimited use of a 39Mp single shot camera with any lens I needed - all free of charge. It meant I could familiarize myself with the system at someone else's expense and without *messing* with my own new camera at this learning stage.
The files from this camera are astonishing, but that's off topic.................
ps. The last time I checked, my 1DsMk3 is a closed system too. However, I admit it does not suffer from any backward compatability - a very, very bold move by Hasselblad. But, as I wrote above, my timing was perfect, so I haven't been caught by that.
pps. The point made above about it being equally incumbent on the likes of Phase to make decent cameras is very well made.
pps. In 25 years in this business, in terms of bangs for my buck/picture quality/customer satisfaction etc., the best camera I have *ever* owned is the Canon 5D. If the truth be told, it would do the job 90% of the time. But, that's VERY off topic!