You don't play Neural when the runner has a full hand. You play it to flatline them. That means Blood in the Water never costs more than Neural. When the runner's at 0 cards, it's free, and when they're at 1 card, it's 1 and 1. You can even score two from hand to kill a runner for 1.
But the real win is that this version of Neural doesn't take a deck slot... not really. It replaces Project Yagi-Uda or whatever other useless agenda your PE deck wasn't planning to score anyway. So you've got an extra non-agenda deck slot to work with.
One downside compared to Neural: the runner can take it from you. But they would have taken the Yagi-Uda too, and you still have that extra non-agenda card.