They might look okay from the outside, but I can almost guarantee that inside they're absolutely atrocious. They're probably not smooth but jagged inside. The bends probably aren't as smooth as they can be, and the collector is probably absolute shit.
There's a reason headers are expensive. Those eBay headers(and almost all eBay parts for that matter) are crap. If companies could produce and sell headers for that cheap, they would. There's a reason quality, proven power making headers are more expensive. There's extensive R&D that goes into them. Countless hours and countless dyno runs go into a finalized header design.
There are some uber-expensive headers out there: Rage, Hytech, JASMA, RMF, SMSP, TODA etc..
But then there are also great products out there that you don't have to pay $1k+ for: Skunk2, Greddy, Comptech, etc..
If you're on a budget, there are also good quality products that only sacrifice <10 horsepower: DC Sports, and especially the DC JDM 4-1 with 2.5 collector, there are some replicas out there of Hytech and RMF, JG Edelbrock with 2.5in collector is good, Airmass(an often overlooked company) makes a good product.
And then there are the random companies that produce headers that have been proven to make good numbers, Kidd Racing, Jerrybuilt, etc...
The cheapest I'd go is Blox or Megan.
Just figure out what your budget is and do a lot of searching and research and decide what you want.
But budget-wise, you can't go wrong with DC.
When I get my next GSR I really REALLY want a Skunk2 header. It's got high-end features found on $800,900-$1000 headers such as stepped primaries, 2.5in collector, both flanges are CNC-machined.
I've been waiting for S2 to come out with a header since I had my first GSR. I thought it was strange that a company that built it's reputation on NA power and racing has taken this long to produce a header.