hee hee
I can say the following without even seeing you fly:
You, my friend, are going to be a fine pilot. If you get a heading hold gyro you will be a fine pilot sooner. If you don't get a heading hold gyro, you will be a fine pilot, perhaps even finer in the looonngg run, but it _will_ take longer.
Myself, I don't think I'd have the patience to do orientation practice without a gyro. That's me, I get discouraged easily. But you have already passed beyond that point, and you have done it without a gyro.
So get a gyro.
You will be glad you did, and you will also be glad you learned without one.

I stopped making sense a long time ago, so don't worry....

This reminds me of the heat-related yaw issue with cx/cx2. I did everything to try to cure it, finally realized that it didn't matter to me any more because somehow I learned, in all the testing I did, to fly the rudder. Now, with the coax helis, I just ignore trim changes and fly the silly thing. I'm not quite at that point yet with the BCPP.

The gyro in the 3-in-1 is in some kind of standard rate mode i guess, the performance isn't that great so it's hard to say. The tail-motor system in the BCPP has a hard time keeping up with any decent gyro (the G90 is fine in my experience, the LHS recommends it over the rce500x). Most people who put external gyros in the BCPP probably stay in HH mode, I know I do.

The BCPP is designed to be useful for acro flight, so it is not supposed to be "stable". It should not be unstable either, and the stability can be improved by taking the slop out of the linkages. What we are striving for is technically called "neutral stability." A stable aircraft is like a marble sitting in a bowl, no matter what you do to it it will try to return to the center of the bowl. Obviously this is undesireable in an acrobatic aircraft. An unstable aircraft is like a marble sitting on top of a bowling ball. As long as it is in place it is OK, but the slightest deviation tends to increase and the marble goes sliding off into oblivion. This is called "divergence". Unstable aircraft need computer assistance to be flown by ordinary mortals. Examples of unstable aircraft include the f117 fighter and the b-2 bomber.
Neutrally stable is like a marble sitting on a sheet of glass. It stops, it goes, it slides, it keeps doing just what it was doing until you tell it to do something else. This is what we strive for in an acrobatic aircraft.

So if you have a bit of slop and poor control response, you can make the helicopter more responsive and less unpredictable by removing the slop and play in the linkages and servos. There is a _lot_ of info on these thrreads about how to do that.

Sorry about the long post. You got me into flight-instructor mode for sure, how do you turn it off, my tail is wagging...
No wait....


( There are several way to actually make the BCPP more _stable_ like increasing the all-up weight, using flybar weights, adding fins, etc. These things do increase the stability. They also decrease the acro ability. Is this what you really want? I didn't think so.)