I'm tending to agree with derek, any powder-metal part is going to have strength and brittleness issues, unless some time in a sintering furnace with impregnation/infiltration materials (copper, nickel) is done. Furnace time is not cheap, nor are the infiltration metals. I'd be willing to bet the caster is just grey iron, so for $10 why not try it.
Another minor problem, that caster likely has a fairly large i.d. bore to hold a pressed-in wheel bearing. Not a big deal if you are ready to machine and press a tight fitting steel plug and remachine to your desired bore size.
I've been pondering buying a decent ladle to melt pewter (or zamak?) and cast my own flywheels. Lead would work too, but I don't like poisoning myself. Or making built-up spoked wheels from pipe, of which I have access to a lot of.
I have a couple of engine projects to work on, but I've been too tired lately, having to do a lot of real work (sorry for the curse word). We're doing R+D on a large cast iron valve, requiring a number of build/rebuilds) which means moving heavy parts around and big wrenches and bolts and impact tools. Then one of the hoist rings got a buggered screw from a poorly tapped hole in the casting, and needed a new bolt with a machined e-clip groove. No biggy, grab a bolt from the bin and turn the groove on the lathe...until a stray chip came over the top of my reading glasses and into/onto my eye. No lasting damage done, but it gave me pause. I need to find some decent safety glasses with about a 1.5 diopter lens on them...or buy or make myself some leather side and top shields to fit a pair of readers.