I'm one of the 100 ft and below people, but only subject to a careful examination of the area for 'Vessel, person, object or structure' both on the approach and in the climb out. Obviously this will need prior planning, so I divide my PFLs (as an instructor) into two types: the 'Surprise' one and the 'Planned' one. The latter is used to hone the techniques of height planning, aiming point, drills and maydays etc, and will involve getting to flare height to prove that the system can work. This requires fairly careful choice of field for obvious reasons. The field will offer the best chance of a successful landing, so the concern of 'what happens if the engine doesn't respond' is low, as we will just land. Hopefully the surface will be good enough to permit a subsequent take off. If not, we will have some explaining to do...
I agree with the comments so far that it is the last 500ft which make all the difference (how many times has an approach to the runway which looks good at 500ft turned into a go around by 200 ft?!), and we should, in the interests of life preservation, be able to practise landing in fields successfully in case we need to do it for real one day.
Once we have mastered the basic techniques, then I will throw in some 'surprise' ones during other exercises, and then the go around height will be dependent upon the area, but planned to be 500ft AGL.