Version 12.1
One bad thing is that there is a lot more volatility in the score, based on whether or not the "scenario" (my terminology) correctly identifies which opponents to activate against. And the score difference can be huge. While in the past the Rumble score was pretty stable after about 2000 battles, I would say it now takes more like 6000 to 8000 battles. Watching the progression on version 12.2, after about 1200 or so battles the APS was around 86.85 (excitingly close to WaveSerpent), but now with 3800 battles it has dropped to 86.50, in danger of dropping below Dookious after such a solid first showing. I still don't think we can say whether or not it will level out above or below Dookious.
It should also be noted that the effectiveness of bullet shielding will be less against top surfers. The score boosts will be less against the vulnerable, and there is more opportunity to lose performance against the non-vulnerable.
I also have to take an extra step in future development. Due to the volatility, whenever I am working on anything but bullet shielding, I have to disable the bullet shielding mode to get more reliable testing results.
I know I am kind of focusing on the downsides here, but I think the upside is pretty obvious, thus I am commenting on the more subtle issues this new mode introduces.
After looking at the individual battles against a number of opponents, I might add that with more testing and time, I can probably improve the scenario to activate a little more reliably against vulnerable opponents. This could eliminate at least some of the volatility and possibly give another 0.2 to 0.3 APS boost (assuming 12.2 holds around 86.5). I will have to create a challenge of shielding vulnerable opponents and collect more diagnostics to see which of my conditions for continuing bullet shielding are occasionally violated and why; then I can hopefully tweak it a bit to make detection more reliable.
I've actually been thinking about this. It's not possible to know how well you can dodge their targeting without risking poisoning their targeting into shooting non-GF0 bullets, which makes it difficult to know against bots that you can dodge perfectly if they are secretly a Hydra, and the 97% is a 30% increase in possible score, or if they are just DoctorBob and the 97% is a 3% decrease in score.