I use a soft lighter, and here is a link to the proofs from a recent shoot shot with it as the main light, the only light, except in the pics against the wall. I used my other lights to keep the background hot.
I like the light, I have limited experience with softboxes, and they do offer directional control, with grids etc.. But the softlighter give a nice wrap around and softens edge shadows, and you can cine foil the center or make grids etc...
As for hotter in the center, I have seen the same with boxes. Think about it in boxes the light is pointing right out the box, hitting a diffusor, or two depending on the box, etc. Here the light is bounced into the diffusor from the umbrella. Also you can adjust the light by putting the umbrella closer or father from the light head.
For the money and with the versatility I think the softlighter is a good product, and plan on buying another.
By the way my lights are old... novatrons, I'm going to start adding bees or whitelightings this year to give me more adjustable range.