Hello. The Standard (walnut grips and polished blue finish) is a very fine version of the of the Mk III Hi Power. Subjectively speaking, it does look awfully good to me. It should perform the same as the lower-priced Mk III or the Practical. It's difference is in the finish.
Adjustable sights can be a good thing on autos including the Hi Power, but I've not been too happy with those on the Hi Power as supplied by FN. They're too high for my tastes. Early ones that had windage adjustments made via loosening one screw and tightening the opposing one simply didn't hold zero for me when set unless I used loctite. I'm not sure what version's being used by FN at the moment. Though the adjustable sights might be too high for my tastes that does not mean that they won't work. Should they be of the older style I mentioned, they can be "fixed" to hold zero pretty easily as I mentioned. It just depends on what you personally want.
The "FM" Hi Power is a licensed copy of the FN Hi Power and is made in Argentina. I THINK the letters are the initials for what translates "Military Factory" or something similar. Though I have never owned one for long-term observations, the ones I have shot over the years have worked. Accuracy has been acceptable as has been reliability. I only shot ones having fixed sights and they were well-regulated from the factory. Finish was not so nice on most, but as they were intended for military use, this was not a priority. Many Hi Powers from FN, FM, and the non-licensed makers are generally not known for stellar trigger pulls out of the box...which is a pity. There are very nice exceptions, but usually a Hi Power trigger is not all that great. Likewise, the FM's I've shot had triggers of varying weight. Some were acceptable with a couple being pretty darned rugged. I prefer the FN-made guns, but were I going to do a project gun, I might very well try an FM-manufactured gun if the price was significantly lower.
Best.