Rate of climb vs. Rate of Descent
A common thing among students being tested is that they try to keep a standard approach into confines, bombing into a footballfield-sized LZ at 65kts. This usually results in a quick-stop 20ft above the intended landing spot, and then a discussion about the height velocity diagram.
The diagram shows the alt/speed combinations from which a succesful flare can be made, landing safely. The extra caution needed when operating in the avoid area, means you have to be prepared to dump collective and try and recover some speed for a proper flare.
On approach into a confined area, I usually teach students to balance a comfortable speed, and a safe speed. Too safe/high speed means they might fly a perfectly serviceble chopper into trees, or do one of the other stupid things associated with non-practical flying. To slow and you lose translational lift, and once again its not practical, and even dangerous if they're descending.
Being at 150ft at 35kts is right in the curve, but you're collective will already be down, and a rate of descent will already be established. Very close to an auto.
My personal opinion is that a passenger safe landing can still be made if the engine fails, and lets face it, if the donkey quits, that is really all that matters. Even if you do a perfect auto, there is a lot of luck involved in putting a machine down without a scratch.
If I remember right, it's been mentioned in a previous thread that the 407 has a max safe climb of 2000ft/min, just so that the blades are still turning by the time autorotative rate of descent can be established.