This is a head-scratcher. The D1 reduces red transmission beyond the H-alpha emission line, specifically reducing transmission around the SII line. Yes, it takes away some red bias, but it doesn't appear to make for a completely color balanced image. Software white balancing is still required, so why not give me all the red signal I paid for when I modified my camera? I may not want my images to look red, but I do want the higher signal-to-noise in the red, in my RGB images.
The D1 might promote contrast in the H-alpha details, by blocking much of the neighboring SII details. Fine, but I still want the P2 filter. If I want to promote H-alpha details, I will shoot through an H-alpha filter separately and manage it in post-processing.
I guess it comes down to wanting a choice.
I am attaching a couple images. One is chart I cobbled together, overlaying the response curves for four filters: the stock Canon IR-UV cut filter, the Baader replacement, the LPS-P2, and the LPS-D1. The LPS filters differ on the far red, with the D1 cutting out much of what the Baader filter added.
The P2 curve nicely extends out to the range of the Baader filter; a good match.
The other image is taken from this DigiBorg blog posting:
That blog compares daytime images shot with a modified Canon using the P2 and D1 filters, with automatic white balance. I further white-balanced those images in software (and even the D1 image needed it).
So my ask is, give me all that red in the P2 filter, promoting SNR, and I'll balance it in software.