Definitely worth investing a little time and money into a Mercury.
A lovely, graceful break barrel from yesteryear.
Usually, the trigger will adjust for a nice, crisp release.
A strip, de-gunk, replacement of piston seal & buffer, breech seal and mainspring combined with a re-lube should see it shooting well and capable of giving good service for years to come. And it's an appreciating classic.
At worst, if there's any breech wobble, you could nip the breech jaws up in a vice. And if you fall in love with it and enjoy it generally, you might invest in a breech bolt conversion.
Protek, Chambers, TR Robb and John Knibbs for any parts required.