Many accessories made for the 870 will fit, as far as 870 parts I'm not 100% sure about but I feel sure many could be fitted if necessary. Barrels won't directly interchange, since the barrel ring is in a different place for the Pardner - it has a 5-round magazine tube versus the 4-round tube of the 870.
Fit and finish seem acceptable to me, but I'm not as demanding/picky as some. I have a couple of Pardner pumps, as well as a couple of the Hawk 981/982 870 clones that Norinco used to import. I decided a few years ago to see how well the imports performed, started picking up various models, and so far they have done as well as the originals. I sat down with my gunsmith, a 981, a Remington 870 Express and a Swiss file, and field stripped both. We went over various parts and he tested the metal with a Swiss file, he said he liked what he felt in the Norinco better.
Some people will object to the made-in-China label, if that bothers you then don't look any further.
They're heavy guns, there's a lot of steel there, but that weight will help soak up recoil from buckshot and slugs. The standard stock is 13 3/4" LOP, a little shorter than Remington's usual, and that will fit some people better. And the synthetic stock is pretty thick-walled and solid as well, the factory recoil pad is decent too. They come with factory sling swivel studs. The forearm is the 9" length field type forearm rather than the shorter 7" LE style, which means if you install a Sidesaddle you'll need to use the 4-round version.
The barrel is 18.5" in length, CYL bore and bead sighted, and overall the gun is a bit more than 38.5" long. It's handy for a defensive shotgun, if that's its main intended role, but the short open choked barrel will not fare as well in some other roles. It'll do fine for shotgun fun on the range, plinking and such, but for formal claybird games it might not be welcome in some venues and might not perform as well as a bit longer sight radius could allow.
I think you could do a lot worse than to buy the Pardner, or spend a lot more money and not do as well for that matter.