Not having flown one, I've been quite surprised to read about the intricacies of the 135's fuel system. Having to push fuel around like this at low fuel states on a small helicopter seems to me to be a design "gotcha", if ever there was one.
I'm glad to know that the airframe fuel system of the small twin I "fly" is far less complex, being almost completely gravity fed. A transverse main tank drains naturally into a pair of 100kg supply tanks. A booster pump for each engine picks up fuel from a sump at the bottom of each of the supply tanks. Fuel naturally gets to those sumps by gravity. Unless you go horsing the aircraft around at very low fuel states (and the FM warns you not to), all but 5kgs of fuel gets to the engines. Nose up attitudes aren't a problem because the sumps are near the rear of the supply tanks. If a booster pump fails, the engine driven pump is entirely capable of sucking up its own fuel. This is verified by the after start checks.
If a helicopter gets to a really low fuel state, the pilot will generally be thinking about slowing down, making an approach, then landing. All of those things require a nose up attitude....... Yet on a 135, this is precisely when there is a potential fuel supply problem. Flawed design, imho.