Ok Mark
I have tested it a number of time to a pretty severe level of pressure. What I can say is that based on the little bit of testing I have done, it would not be my preferred connection for a bimimi to a twisted leader and i would recommend you against using it. The problem with this approach to attach a twisted leader is that the pressure is not spread evenly along the full length of the connection. it is focussed at a single point around the twisted leader. I have attached a couple of photos which I hope can show it.
The first photo shows the attachment before any serious pressure is placed on it.
The second photo show the attachment after some really serious pressure has been placed on it. Unfortuntely, the damn thing looks almost exactly the same! What I suspect would happen did not in fact happen. Unfortunately though, what happens is that the bimimi only really tightens around the highest point on the twisted leader. In effect, the rest of the wraps around the twisted leader are pointless. I tried to attach this on a number of occasions to get it to tighten throughout but could not get it to do it nor do i think this is possible the way this attachment is made.
In a lot of ways, this has parallels to people to tie a really long FG knot. It is actually pointless to do so because the FG only tightens against the leader for about 1/5 the length of the FG knot. The rest of the knot hasn't bitten into the mono and is useless.