the j12 might be more accurate than the noob out of the box, however, when building a franken you will replace the dial, tachy, hands, dw, cyclope and crystal anyways + the case will be totally reworked. In general i prefer the noob case since the gen and most quality aftermarket straps fit way better on it than on the j12 case + as far as i know there are for example safaris or pandas of the old generation with F serial (noob caseback) but not with I serial (j12 caseback)... J12 is great as a base when you are looking to built a franken on a bracelet, want to have one with blue rubber crown/pushers or maybe building a rubber clad (if the new rubber bezel is really that good)...