I have the Grizzly version. It is so similar to the original it's clearly a duplicate. There seem to be several brands of these and they're almost certainly made in the same factory. At least one older version has a solid knife, most have two knives. Sharpening is not that hard to do. Flat ground with a slight bevel on the back. I'd sharpen it with a flat diamond stone.
Lots of posts on here about removing rust. You may not really need to replace the springs. I use mine mainly for cutting picture frames and cannot conceive of making a proper frame without one. I also use it to cut an exact 90 on face frames. The more accurate the cut, the more square the faceframe will be.
Easy to use. Cut the workpiece about 1/8th too long and trim off about 1/16th from each end. Do not try to cut more than 1/8th off, it's a trimmer which perfects the cut, another saw makes the rough cut.
For frames, the key is to make certain that both oppossing sides are exactly the same length. Grizzly makes a couple of aluminum pieces, one with a movable stop, to help do that. However, they are relatively short and I seldom use it, and prefer to measure the two pieces side be side, vertically, on a table. I cut the first piece to length. Then cut one end of the second piece and use that as a starting point for measuring. Use a knife to mark the cut point on the short side of the miter cut (the outside is not visible in the cutter), then trim to that line.
When sharpened (you can send it to the address in the pdf Stick posted), it will do a very fine shave, up to about 1/8th. More than that and the blade will tug on the piece and possibly mess up the cut. You must hold the piece firmly against the small fences or you can wind up with a curved cut that won't close.
I mounted my trimmer on a chunk of ply with handles at the balance point. this keeps me from getting anywhere the blades. Sharp doesn't begin to state how viciously sharp those blades are. I keep a piece of cardboard in place over the blades so I won't ever reach in there again. NEVER get your fingers anywhere near those blades!!!!!
You are lucky to get your hands on one of these. I read that it was first produced in the 1880s, and no tool will stick around that long without being best for the job.
Again, Stick's pdf has all the information you need. Enjoy.
The more I do, the less I accomplish.