This is a good vice for holding your work for filing, though there are better designs, but it is the wrong type to use in a forge. For that you need a leg vice. A leg vice has a leg, of all things, that goes all the way down to the floor to transfer the force to the ground. Also the treads on the screw do not contact threads in the frame but in a sleave that's loose inside the frame. That keeps the screw from being ruined by the force of hammering. The jaws of the vice are opened by a flat spring. However, even these are a poor substitute for an anvil for most applications.
I think that the jaws on the vice that you are looking at would get in the way of your hammer as well as not having enough mass under your work besides being at risk of breakage. See if one of the sites on Ebay sells a steel post about 3X3, 4X4, or 3X4 or even 3-5" round and about 1.5 to 5 feet long and set it in a tub of cement on end. This would be better than a rail road rail anvil, unless you can get the rail for free, and much better anvil than the vice that you are looking at and probably won't run you much more. There are some smiths who prefer an anvil like this to a clasical European style anvil.
Doug Lester