I have a Merkel 140 in 450/400 3" (.400 Jeffery) and a Chapuis in 9.3x74R.
I like them both, to point of not having a 'favourite' per se. Naturally the task at hand will have me lean toward one over the other as required.
I don't see any meaningful variation in fit, finish, visible build quality between them.
I prefer the forend styling on the Merkel (more 'British'), but the Chapuis has nicer timber.
Neither have required any repairs, the Merkel has more time in the field, no issues. I have taken a few buffalo here with it. It is considerably heavier, of course, accomodating a larger cartridge, and accordingly on a bigger action, but handles well.
I've been able to get slightly better regulation out of the Chapuis, < 2" @ 50m. Have not been able to replicate the two shots / single hole of the factory test target, even using the factory ammunition they used.
But the Merkel regulation is certainly serviceable, ~3" @ 50m so far. I have to try one more powder (2217) with the Merkel, more effort may tighten regulation up a bit.