The Micromac website appears to live on long after the company is trading...
From my researches, I conclude that accelerators may be ROM version dependent. A Plus accelerator should work in a 512Ke, but not necessarily a 512K or 128K. Unless you install 128KB ROMs. A couple of manufacturers made accelerators that worked with both 64KB and 128KB ROMs -- Newbridge products are interesting, for example.
From my researches, I conclude that accelerators may be ROM version dependent. A Plus accelerator should work in a 512Ke, but not necessarily a 512K or 128K. Unless you install 128KB ROMs. A couple of manufacturers made accelerators that worked with both 64KB and 128KB ROMs -- Newbridge products are interesting, for example.