jpdenver,
I have both a Delta 4x36 belt sander with 6-in disc. and a Harbor Freight 1 x 30 belt sander.
The 4x36 was originally acquired for wood, but from the beginning was used for all materials. Before that I sometimes clamped my 3x21 portable belt sander in a vise and (carefully) used it for forming and smoothing small parts. (I know, risky.) I can't see a shop without something at least this big, as the usable area of the belt with good flat support behind it is actually more like 6 inches long.
Unfortunately, sometimes the belt and disc on that machine are too large for smaller parts, so I got the 1 x 30 and began modifying it to fit my needs: That experience, still not complete, is described here:
http://www.homemodelenginemachinist.com/showthread.php?t=17108&highlight=Belt+Sander
The 1 x 30 you want has the disc attachment, but I think the belt part of the machine will be similar to what I have.
After the experience with the 1-inch wide belt, I have considered that perhaps a more-powerful 2-inch wide belt might be desirable. If money were not an issue with me, I think a would purchase a 2 x 48 machine like this:
http://www.use-enco.com/CGI/INSRIT?PARTPG=INLMKD&PMPXNO=953354&PMAKA=505-1370
This is made for metalworking and would probably last forever in my shop and stay in adjustment.
I have followed Chuck Fellows's build of a horizontal 2-in belt grinder and am contemplating that as a future build. Find it here:
http://www.homemodelenginemachinist.com/showthread.php?t=22566&highlight=Horizontal+Belt
Finally, my real criteria includes these points:
1. What size work will I most often do and can I do it within the parameters of the machine I want?
2. Lots of different grit and type of belts will be needed: How hard is it to change and align a belt? How are discs attached?
3. Grinding and smoothing specific angles requires accurate tables and guides: Does the machine provide these and/or allow for easy adjustment? (See Bazmak's modifications)
4. What grits and finishes of belts and/or discs are available for the machine you want? Check tool vendors for selection and prices.
5. Will dust be an issue? Is there a provision for dust collection?
6. (At least for me) How many ways can I hurt myself with this machine? What kinds of guards and safety features do I need and can I use them?
Happy shopping,
--ShopShoe