Did a little research on the Model 90. Seems to be made 70 years ago or some where in that area. As for price they are all over the place running from a couple hundred to five plus depending on condition. If it were me I would stop at a gun smith and have them check it out. Since we are talking 16 gauge if you don't reload shot size is limited to 2 or 4 from Federal. But the speed is dismal. Limiting your shooting range. If you reload, BPS has a nice load with 7/8 oz loads that have nice speed 1550 fps and you can use any small size shot. The loads are just as low or lower than lead loads in the psi range, 9800-10,000.
I happen to use a 16 gauge double that is from the 30's and I shoot steel through it. Not a lot of shells maybe 2-3 boxes a year. Usually use it early in the season when woodies are the primary target. If you are concerned about steel you can go the Bismuth route but shells are going to cost you in the $30 a box range. I only shoot small size shot 3's and 4's. I do load a few shells for the occasional goose that happens by with 2's.
If I own it it would be used in the swamp, BUT that is me. Your not dealing with high pressures, wads are heavy enough to protect your barrel, and they are fun to shoot. You will have the nay Sayers say not to use it but altimately it's your decision.