I'm not talking about any one part in particular i guess.. ALL the parts aren't of the same quality as their OS counterparts. Do a test. Dismantle both engines completely and lay out the parts next to each other on the table. Then go get your wife/sister/mum or whoever knows nothing about nitro engines . Ask them to pick which parts look the best quality. You will end up with a pile of OS parts and all the arrow parts leftover.

I'm not totally concerned with appearances though but these things need more attention for me: The groove in the slide, the inside of the cooling head, the exhaust port in the case. Also i'm not sure what the slide is made from but it I think its aluminium whereas the OS one is steel(could be wrong about that).

I'm not trying to "eat my own" as you put it. Just pointing out that while the arrow shares many of the dimensions of the vspec, it doesn't share it's build quality. Don't get me wrong I quite like my arrow.. But if they want to sell big numbers and compete with companies like Alpha and Go, they will need to improve the overall finish.