Mate, 25" barrels go off like a howitzer & are not generally appreciated by hunting buddies. As a big fellow I also feel them to be stubby, coach gun like.
If that Webley had 28" or 30" barrels I would be on to it as long as it was no more expensive than the Merkel. But that is only due to my romance with British guns.
You did not mention weight & that may come into it if you will be carrying it a lot on your bird hunts.
Both BLE.
Both have straight grip.
Both have double triggers.
Both 12g
Both fit & handle similar.
Both choked the same.
All these things I also like in a gun, but I also like the 3" chambers & 28" barrels of the Merkel.
3" chambers because of the versatility they give you in being able to shoot soft loads & hard.
Does the Merkel have the fleur de lis proof mark for steel shot & a 1350 bar proof. If so that would be the clincher for me because then it can be used if you want to go after ducks.
To me the Merkel seems like more gun, & I like more gun sometimes. If you buy a less of a gun, then you can not safely use it as more.
I could put up with a Teutonic gun If it gave me enough more.
Which one speaks lovingly to you when you hold it ?
O.M