alright im going to go out on a limb here and say they are the same manifold. I'm looking at them in pictures from rhdjapan, and nengun, and they like the same manifold. same little "support" pieces on the bottom of each runner near the main flange, same bolt on support bracket for the turbine flange, everything. Yashio Factory is a great brand, but they (he) tends to be a little pricey. Being a smaller shop, not every part may be made in house, possibly even that manifold. I've watched a bunch of Sammit's videos when he's in okachan's shop, and it doesn't look like there's a level of production fabrication going on, it's more bespoke...so it may be a real possibility that gp sports is making them to his specs. It's hard to say for certain. RHD Japan lists more specific feature on the gp sports manifold, and y.f. just has nice pics and a price..so it's hard to be 100 percent on it (maybe this is on purpose?)
Either would be fine, both would be susceptible to cracks like any other manifold (especially that design with multiple welds for each runner...not saying it will, they are both quality pieces, but even the best manifolds sometimes crack, just the game we play..). Either would get you brownie points at a show, and both look super cool jdm yo!
Would you consider a third option? I've always thought about running a FullRace manifold, if my tomei decided to shit the bed one day. The manifold is at the same price-point as the JDM ones, but with a little something extra..easy to reach tech support and a stateside phone number for warranty issues. I've met Geoff Raicer, the owner of the company, and beyond being super nice, his level of detail and craftsmanship that go into those manifolds is unmatched by anyone else that I've come across. Now I know this isn't a "super cool jdm" part, but its still an amazing piece that not a ton of people rock, and is still made by a great company that means a lot when people see it. If I were a judge at a show, I'd be impressed.
Sorry about the large image, taken from their website.
Link to the part:
https://ffperformance.co/product/ful...iABEgIUkfD_BwE