I've heard they're reputable, but I wouldn't preorder a product that far in advance from eBay no matter who it's from.
1) You're pretty much screwed if you pay in advance and the company folds between now and when the product comes out. You also have no recourse unless you paid via your credit card and they back you up (again, 6 months or whatever down the road)
2) Refunds if you change your mind and no longer want the product? good luck - depends on the seller's willingness. Not speaking for anyone else, but happens to me all the time.
3) There will be TONS of sellers who have this product for sale before, during, and after release. No need to order it and prepay immediately with the "gotta have it NOW!" mentality when you
can't get it now.
4) If you hold off and order through Sideshow, you can also support this message board we all love
That said...not dissing anyone who chooses to preorder this far in advance through eBay, it's just really not for me. There's no danger of not being able to find it at release or through Sideshow.