With Yadif it might appear a bit sharper, but it's often more artificial than real. From VQEG's "Mobile" sequence:
TempGaussMC(Yadif):
- TempGaussMC(EEDI2):
- TempGaussMC(NNEDI):
If you switch between them, it's quite obvious that Yadif's speed comes at a price, and that NNEDI spends its time quite well.
Now that's an extreme example, it's possible that you won't see much of that on the "average content". It's just when using this script *always* with Yadif, and you're occasionally experiencing those artefacts, remember that it's not the script's fault, but your choice of having more speed.
BTW, I like EEDI2 pretty much in this script. Not
quite as good as NNEDI, but pretty close. When dealing with interlaced content a lot, the small differences to NNEDI could be very well worth the speed gain.