The Ultrafine, and Ultrafine Plus, both appear to be different manufacturers based solely on packaging. My guess would be Chinese for one or both of those lines. I have never tried the official GP3 film, but I have read the curl is similar to what I saw.
The Extreme line is a relatively new animal, and that is the one that has "Ilford Like" packaging. I ordered some real HP5 in 120 today, so I will do a direct one to one comparison of the Extreme 400 in 120. The 35mm product may be a completely different film as well. I just haven't tried it. Other reports on Flickr of the Extreme 100 in 35mm seem to be favorable, but it only comes in 35mm.
FWIW they also have a couple other items that I personally have been very happy with for the $, I am hesitant to even draw attention to what stock they might have left. I plan to stock up while I can, but who knows they may have a couple metric tons of this stuff. There is an off label APX100 35mm 24 exp rolls at $1.49 (I have tons of bulk APX400 so I haven't tried it myself but they have it for a dime more per roll). The other is "Chromogenic 400 B & W C-41 Film 35mm x 27 Exposure" for $1.59. Granted this is the only pseudo B&W film I have tried, but I personally loved the look. Any ideas on who could be making this stuff? I only know of the Kodak and Ilford brand C41 B&W.