In the course of googling to help resolve nandboot confusion, I found what appears to be an alternative of sorts. Obviously, Nand Manager dumps NAND, however it's geared more for firmware switching than backups; it apparently takes 20 seconds to go from 5.50gen to 5.00m33, for example, and going back to gen is just as fast. Apparently it compares backup to nand, block by block, and only writes if the segment differs. This is safer too, as it reduces wear. The files are compatible with the nand tool in universal unbricker.
Naturally 1.50 is out of the question, OFW is off limits, and this provides squat compared to a Pandora when it comes to restoring from disasters, but I figure alot of people just want to switch between the two popular firmwares. Barring power loss or > 100000 swaps this seems a safe alternative, (unless the PSP's nand chips are crap compared to those in HTC G1s; I swap firmwares alot on my phone).
Plus it's not on qj or psp-hacks, so blah blah blah - oh, I'm done. Url time:
Official homepage (jp): NAND Manager / Adhoc File Transfer
(google translate): Google Translate
English forum with description: 5.00 M33-6 and 5.50 GEN-D3 on a single PSP without Pandora Battery!