I picked one of these up a couple weeks ago. I've not yet had the time to do other than a very cursory function-firing, but I'll share my impressions. Like you, I am not overly enamored of the ports. However, they don't seem to hurt anything. I didn't notice any excessive report or blast. I haven't yet tried to determine the accuracy possible with this piece, but it seems to hit typically for such a carbine. My funtion testing consisted of shooting offhand at a 3" orange aiming dot at about 30 yards. Most all the hits were on the dot and those that weren't were when I goofed my trigger control.
I obtained the piece to replace a similar Winchester M94 "trapper" that I sold because it wouldn't handle lead bullets...shooting "patterns" rather than "groups" with same. The Marlin 1894-P has "Ballard" riflings, which is supposed to handle lead bullets. My limited testing indictaes that it will. I did notice a tendency for the shoulder of SWC bullets to catch slightly on the chamber mouth, interfering with smooth cycling. Cycling was smooth and positive with "shoulderless" truncated cone bullets.
All in all, the piece looks promising. It is very short, light, reasonably powerful, and has a decent magazine capacity. I plan to add an Ashley Outdoors' aperture sight & square-ramp front, a light nylon carry strap, and perhaps a butt-cuff for additional ammo.
Rosco