Two different design approaches.
Both basically use two fixed and one moving point to bend metal, but the designers really came at it from different directions.
A Di-Acro has a big, machined circular plate for a base, with precisely drilled holes in it.
It was based on a tube bending philosophy, with a design that supports a three piece tube bending die setup, which makes for nice, evenly supported tube bends. It is more of a small scale, precision bender. A Di-acro is usually smallish, althoug they did make them up to a number 4, which is pretty big, and even a number 6, which was a power version. The most common ones, though, are 1's and 2's.
Nonetheless, even a number 4 Di-Acro wont bend as big of material as a hossfeld. A hossfeld will bend up to 4" wide or 4" diameter material, although for some larger stuff, it has to be done hot- but anything that will fit in the frame, a hossfeld will bend.
A Di-Acro number 4, on the other hand, tops out at 1" round bar, as recommended by the factory.
A Di-acro is also much more limited in the types of profile it will bend. Solid Square and Round, flat bar the easy way, and small tubing.
A hossfeld will bend angle, channel, T bar, square and round tubing up to 3" or so, pipe, solid square, round, flat, hex, flat bar the hard way, railing cap, and just about anything else.
So I would say a Di-Acro is more a small scale, precision bender, while a hossfeld is a slightly looser tolerance, multi faceted workhorse.
And a Di-Acro, because of the way its made, costs more for the basic machine- 1200$ to 3000$, new, depending on size.
A new hossfeld is only $800.
But with a hossfeld, you could literally buy another ten grand worth of tooling if you wanted to, while there just isnt that much tooling available for Di-Acro's- different size tube dies is about it, as far as optional tooling.
Which is not to say a hossfeld is not accurate- with degree of bend stops, and depth stops, a hossfeld can do things like bend 20 foot long pieces of 1 1/2" square tubing into 40 foot radius curves (my carport roof) repeatedly. Or hundreds of multiple bends in 3/8" round stainless, all the same.
Really, you need both. And not just one Di-acro, either- it would be nice to have a No. 2 and a No. 4 as well, in my opinion, to go alongside my hossfeld.
Di-acro benders-
http://www.diacro.com/manualBender.htm