Actually the PCE-500 is much better than the PCE-220, they are not in the same league. Strange that you don't like the 500, it is the top of the line for Sharp Basic machines (and all Sharp machines for that matter...).
The 220 has a Z80 processor and an embedded assembler, it is very much oriented towards ASM. The machine is much thicker than the 500, being made with a less classy plastic. Also, the display sports plain 5x7 character matrices (four 24 char lines I think) with no graphing capability. BASIC is standard with no extra features like a built-in library.
It has a calculator mode, quite like a scientific calculator (like the PC-1401 or PC-1403).
I think I recall it has a built-in RS232, but this is the only thing going for the poor beast.
If you are a collector anyway, prepare for a long search (albeit your question seems to imply that you found one), because it is much much rarer than the 500. So get it, but don't expect too much.
HTH.