1. Superior movement for the SBGD, conceived and produced by the Microartist Studio. Accuracy is sthg that can damage one’s interest in non SD movements, plus the sweeping seconds is very unique
2. Overall design (case, crystal) quintessential Seiko, so for me more authentic. Plus more sculpted and hence more attractive (to me) than the Eichi
3. Insane level/quality of execution, eg crystal, dial, hands, movement materials (German silver, baseplate thickness, etc), movement anglage, etc. One of the top three independents has told me that the level and consistency of execution cannot be bettered by any other team in the industry
These would be the main reasons. And maybe also the rarity. I think both are rare but the numbers I know from GS about the SBGD are so low it feels even more special than I already think it is.
Don’t get me wrong, I do love the Eichi though and I did consider it many times!