Is this a good hps hood fixture?

http://www.igrowhydro.com/Package-Parabolic-HPS-400.aspx

(I hope the link worked)

Do you think this umbrella like hood fixture works well?
Or would a rectangular shaped one work better?

I don't see why it wouldn't work well. It depends on the size of your grow area, I chose a rectangular hood because it just works better in my closet, that hood would be kind of awkward in my closet.

I've never heard of them before but the umbrella looks cool. I personally am using the lumitech ballast thats at the bottom of that link you posted and its cheaper. For 168 shipped I got a switchable 400 watt hps AND mh sustem that came with a free hps bulb and a free mh bulb.

Here yah go
http://www.amazon.com/Ulti-lumenx-Pressure-Sodium-Electronic-Digital/dp/B004YXDLCS/ref=pd_ys_iyr_img