I have an Argentine FM hi-power. It's the earlier production (i.e. surplus) rather than the new production offering of late. Both can be found if you look. The current one has a different slide profile on the front end than the older, FN-type copies like mine. I don't care for the new style, so you may want to make sure of what you're getting if you buy an Argy. It would be disappointing if you thought the gun looked like one version, but you actually bought a different one.
I'd recomend saving money and buying a MK-III as well. The MK-III is a much better gun overall. Quality is as good as it gets, and the sights, controls, etc. are all more refined.
Now my Argy has a few mods, and will get a few more, so I'm not really worried about being outclassed by an FN. But to take a NIB Argy and bring it to the level of the MK-III would cost you more than what you'd have to pay for the MK-III in the first place.
In the end, the Argy (even a new one) is on the same level as any surplus gun. The MK-III is on the same level as the newest production wondernines. If you just want a blaster, the Argy will be fine, but if you can get the MK-III, you'll find the extra cost to be worth far more than the cash difference.
The Detective model you're looking at also has a slightly shorter frame as well. You might want to handle one in person first.
Ross