I personally would not make that trade unless that marlin has been sitting in that box in someones closet for quiet some time....and it doesn't look like it has, so no.
The 686-2 is a prelock S&W, and is quickly becoming collectible as a gun that still retains some of S&W's former craftsmanship as opposed to their current production guns.
The Marlin, if it is a newer one like it looks to be, is quickly gaining a reputation as a sad shadow of the former marlin production quality. I have lost interest in the marlin .45-70 guide gun due to rampant reports of poor quality in newer production guns. Since it is new and unfired, you have no idea if is a lemon or not, and many of those were.
You would basically be going from the pinnacle of S&W handgun technology,
To the cheapest, worst quality era of gun "marlin" has ever put out.
If you do decide to make that trade, at least make sure the marlin chambers and ejects shells well, bring a few types with you. One of their main issues was feeding problems.