Thanks for the reply, Luap.
I agree that they are overpriced, but they are not nearly as complicated as you suggest. I have personally disassembled and inspected the design of all but the hensel model.
Both the Broncolor Picobox and the Profoto Probox are designed to receive a head via their standard mount. You could put a probox on a pack-based head, or a monolight just as easily.
The design of all of them is essentially a box made of 1/8" white acrylic, with some internal piece of metal to block direct light on the face (similar to a beauty dish). The probox also has 4 triangular pieces of white plexi in the rear corners to bounce the light forward around the metal disc. The entire unit is held together by a very thin sheet of metal. It is quite simple, and much lighter than anything made of plywood could be.
The Broncolor Boxlight is similar in overall construction, but it has two internal linear flashtubes, spaced at 1/3 intervals with a small strip of thin metal in front of each one so the light is directed every way except forward. I imagine Hensel use a similar design for their model.
The Omni solution you suggest would not work for how these lights are used. It isn't just an even square (actually rectangular) face that is desired, it is the small size so it can be placed near a tabletop set to produce specular highlights in the product. Since the goal is creating specular highlight quality and not diffuse illumination, there is room for a little inefficiency. In my experience though, the power lost is not significantly worse than other popular modifiers. It helps that they are small. The round edges of an Omni would also be obstructive because these lights are sometimes placed right on the table surface. You can see an example of that in the video here:
http://bit.ly/XU87lbAs for the cost of shipping... The profoto unit weighs only 5.6 lbs, including the bulky light mount. The Picobox, which is physically a little smaller, weighs only 1.87 lbs. Neither one is particularly fragile.
Speaking on behalf of product photographers, there is quite a market for these. I have assisted in many studios who have bought a whole broncolor pack, pico head and a picobox, just to have access to this essential type of modifier.
That said, I would be much happier to see attention devoted to a handle and/or a modelling light switch on the e640, so I don't want to derail that conversation. I just figured if there is any company that can produce a well-engineered, simple modifier for far less that the overpriced competitors, it is you guys.
-Russ