HP A646 Compact Photo Printer Review
Polaroid Z340 Comparison
Perceived value of each printer has largely to do with what you value in a printer. If you're looking for instant prints like the Polaroids of old, the new Z340 is a great pickup. It can't perform on the level of the HP Photosmart A646, but it does provide you with convenient and quick prints. If you want something you can hang or frame, you're going to want the HP Photosmart A646 instead.
The Polaroid has a severe problem with color accuracy, though it's not much of a surprise because the printer uses no ink! Regardless, it did not fare well in any of our tests.
The Polaroid has extreme difficulty maintaining detail on its tiny 2 x 3 photo paper, but to be fair, it does not have thousands of tiny nozzles blasting its paper with picoliters of ink. It has no ink at all, so there's really no reason you should expect it to do as well as the HP Photosmart A646 for this purpose.
Though both are convenient compact printers, you really have to determine what you want in one to decide which is the more fitting for your use. If you want instantaneous tiny prints with dubious quality, the Polaroid will rekindle your nostalgia for their older cameras. If you want a versatile compact printer with decent quality, the HP Photosmart A646 is going to seem more usable to you.