Okay, the Defiant and Equinox I ordered off eBay finally arrived today. (I was rather annoyed that the Equinox's stand was broken, but that's another matter).
The Defiant's got some really good detail, but I feel like the overall shape's not quite right. I feel like the Micro Machine one's dimensions are a bit better. I took a picture holding the MM one close enough to see how they'd roughly look at equal size:
The lighting's not that great (sorry, not that great a camera), but you should be able to notice some differences.
There's two main things: 1) The aft section and the nacelles on the Furuta Defiant are oriented straight forward, rather than being a bit diagonal. 2) The nose section is noticeable longer and narrower. It also doesn't point down as much as the MM one does.
These two things make the ship appear a bit longer and slimmer than it should probably be.
Apart from the stand, I much happier with the Equinox. I'd forgotten how stubby it looks from certain angles, but I feel like those proportions are right. The only things I don't really care for are these grid lines on the sides of the engineering hull. They look kind of shoddy, compared to the rest of the model. At first, I actually wondered if a former owner had painted them on until I managed to find a picture of the model's underside on Google, showing it was indeed made that way.
Well, still worth it, I think.