The main danger with a constant speed approach IMHO is that the faster you are going at the bottom, the more flare you are going to need to stop. In some landing sites, you really dont want a big flare because: A) you put the tail closer to obstacles/ground and B) raising the nose can impede your forward visibility towards the landing site and obstacles in front.
That is why most manufacturer-designed profiles for helipads/helidecks/confined areas will take you to a decision point at the minimum possible speed where you are going to still have enough power ( in a twin) to fly away if you gat an engine problem up to that point.