Pongo,
I understand your frustration with this little heli. She is a fragile little thing. For me I have had the best results troubl shooting things by bench testing.
I either strap the thing down or hold the tail just behing the frame (very tight) and crank her up. give all sorts of different inputs on the Tx and just observe very carefully. I also usually do some spool ups with no blades to ensure that that things are in balance and that the flybar is tracking properly. Then if that all seems good. I double check the blade CG & balance. then put them on and start with the bench test observations to look for anything that just doesnt seems right.
I must say you are lucky you have other heli's. This was my only one for a year. I just bought a mini titan so windier days here I come.
There were many times I wanted to stomp on this bcpp. I usually recovereed by stripping the whole thing down and inspecting every part for wear and slowly reassembling it part by part. [:@] I would do spool up test all along the way to test each faze of assembly for balance/vibrations.
Also I agree about bling and mod's I stick to simple and cheap for this little thing. I did go DD a long time ago and that was worth the effort for me. I also bought a cheap telebee HH gyro. And most recently put a slow-max motor in it when I cooked the last stock motor. Other than that I dont spend money on this heli unless it has a broke stock part and then I will replace it. Bottom line though, imo, this is the coolest tiny 3d capable heli out.
For flight performance, bigger is always better. If someone wants to trade me a 90 size nitro for my blade I'll take it anyday. But I dont have $3-4000 so I stick with small electric for now.
this little thing is really at best a fun capable indoor or backyard flyer. Unfortunatly my lhs and eflite marketed it as some sort of end all-be all heli. Once I got over the frustration of it not being that, I enjoy it very much for what it is.

Good luck trouble shooting, as troubleshooting sucks very much. Noah
P.S. Keep a close eye on dapeners, mixing arms, and flybar setup. Most of my mystery probs were usually me overlooking flybar probs. once I even had one mixing arm flipped over and couldn't find that for several flights of poor performance