From what I have found ..... Hobbywing is the manufacturer with Speedpassion (GT)and Venom(Pro Brushless ESC) both sourcing their products from them. Hobbywing do have there own branded ESC available as well although it may be more difficult to find in some places.
Being made in the same factory doesn't make them all exactly the same but they are likely to share some components and operate in a similar way
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Before saving a few $$$ remember to think about the after sales service if something goes wrong on the ESC. From reading the other Speedpassion thread I can see the folks at Schumacher USA are getting right in behind Speedpassion and are very helpful to all questions asked... I don't know too much about Venoms service so someone else can say if they are the same.