I extensively used the EBC Fujinon 55/1.8 (thread mount). Both the older non-EBC and the EBC are the same optically. I had the EBC (multicoated) version, and it was excellent- sharp, with great color and contrast. Its resolution and nice bokeh make it good for up close and when reversed for macro. It's all I used for several years.
I wouldn't hesitate to get the non-EBC version unless I wanted to shoot into backlight and maintain highest contrast. IMO the 55/1.8 is better optically than the 50/1.4, and stands well against any other normals I've encountered, like the 50/2 Nikkor.
The non-EBC version (satin chrome aperture ring) will mount on any M42 body. The EBC version has a small projection on the back of the aperture ring for open-aperture metering on most bodies later than the ST701. That projection will contact the face of the mount flange on some non-Fujica M42 cameras (and K-mounts with thread-mount adapter). If that happens, either the lug can be filed off, or a body with a narrower (smaller outside diameter) flange could be used. I have a Ricoh with a 54mm O.D. flange which it clears by what looks like a half millimeter or so. I think it would just clear a 55mm O.D. flange.