If you are working with small pieces of hardened steel the surface grinder is appropriate. Can also be used in a manner to attain excellent bright finishes.
However, surface grinding is very time consuming compared to planing or milling processes.
Also, in the USA, used shapers (etaux limeurs) are available for relatively low cost compared to a working automatic surface grinder in decent shape. Tooling for a shaper (the cutters) are cheaper than any other machine I can think of.
I have an industrial widebelt sander (Martin/Tannewitz)in the wood shop. I have run one in a factory used for strictly steel parts. As Jeremy relates, they are not a simple machine to set up for metal including fire suppression. Very costly to operate on an hourly basis. (Air, electricity, abrasive belts, swarf extraction, constant maintenance.). Always keep in mind that aluminum + ferrous swarf mixed = thermite. The machines are used inproduction primarily for surface finish, not calibration (not for sizing or making parallel)
A type of surface finishing machine that is inexpensive in the US is a stroke sander. These will smooth & polish surfaces but will not calibrate. They take up a lot of floor space in the shop. I use mine for wood & sometimes metal.
Good luck.
It would be interesting if you post your eventual resolution or show pictures of what you are making.
smt