At face value, both of these cameras do the exact same thing. They let you mount all sorts of lenses in front of your MFDB, however they go about it in vastly different ways.
We can all agree, that the machining and precision in making the Alpa camera is "masterful" but by no means should that discount the Hartblei Hcam's build quality, which is equally as solid, although possibly not as pretty.
The Hcam is its own camera, functioning with a shutter, and lens mount. The Alpa can also be this (with the use of the proper adapters and spacers), but it is also an accessory for the Alpa 12 series of cameras. Within the modular universe of Alpa the FPS can be mounted to the rear of (for example) an SWA and be used that way. It also has a number of different mounts available for medium format and 35mm lenses. Many, if not all of these combinations are possible on the Hcam as well.
The Alpa, offers the user access to the programming of the camera (but I believe the Hcam can as well). The Alpa also features a (removable) hand grip and shutter button. This seems sort of strange because one would think that these cameras are going to be used on tripods all the time anyway.....Personally, I found the Alpa FPS to be far more compelling when I saw it without the handgrip, because this makes it much easier to pack and carry in any kit.
Both cameras are featured as being usable in the field in all sorts of conditions, but lets focus on cold weather. The Hcam features large soft buttons which are meant to be able to be easily used in cold weather. Conveniently, I had it for testing in the middle of winter, so I can attest that it can be used easily with gloves on (even if an IQ180 can't lol, but then I discovered touch screen gloves so its all good). The FPS has large enough harder buttons which seem to work fine. Personally, the menus of the FPS seem to be slightly better thought out and feature rich then the Hcam.
The Alpa also introduces a control wheel into the mix, which can be used for making some selections and changing variables on the screen. Although it may seem small in some pictures, I think it is large enough to be usable without being too finicky.
However, I do enjoy that the Hcam has two different screens with the top screen controlling the aperture of the lens and allowing you to stop it down and open it back up for focusing. This brings us to another point. Alpa users seem fine with their method of focusing...either using a laser rangefinder, or inserting a ground glass for focusing and then placing the digital back on the camera. The Harblei offers a sliding back, and much easier composition. The sliding back allows for the camera to be precisely placed in line with the lens every time (because it is electronic)....more so then the motor of the sliding back, the fact that it can use Hasselblad V viewfinders for composition is very attractive and allows for a more fluid working process, in my opinion. I believe Michael said in his review, and I say in mine, but the standard Hasselblad waist level viewfinder is one of the better options. But of course you can use all of the PM and PME viewfinders as well as focusing loupes which can mount into the slot (it is provided with one).
A number of the Alpa FPS's features have already been done in the Hartblei Hcam B1 and its variants. There is the B1i and the B1v and the B1iv. I am not 100% certain which is which. But one of them has a sliding back and takes technical camera lenses, and the other doesn't have a sliding back. Then there is the B1iv which does not have a sliding back, and takes technical camera lenses....this is the most Similar to the Alpa FPS.
The Alpa FPS is most attractive to current ALPA owners because it is already integrated into their system, for the most key features of the system, the Hcam offers everything you need in terms of an FPS shutter.
They both use the same Mamiya shutter, but they are mounted differently (in terms of vibration reduction).... as I said before, I hope to be able to do a comparison between the Alpa FPS and the Hcam B1iv (and a copal shutter) to compare vibrations when taking a picture.
Also the Hartblei has a hotshoe...and the Alpa only has a coldshoe... http://brianhirschfeldphotography.com/2012/02/24/in-depth-review-of-the-hartblei-hcam-b1/