Parkerized finish I think.
It may not be parkerized... Many of the cheaper guns that appear like a parkerized finish are, in fact, called "matte blued finish". Which means they are not rust resistant and can be harder to wipe dry than a "polished blued finish".
Parkerized is an expensive finish to put on a gun and not often found on "price point" value guns.
1. Is this a factory length barrel?
2. Is this legal?
3. Anything I should know about this particular gun?
4. Did I do ok at $175?
1.) Most likely,a close inspection of the muzzle crown will show if it is a factory cut or professionally done. If it is a "Bubba Barrel" it will be obvious under a magnifier lens.
2.) Yes, Federally! Some rogue jusisdictions may not allow it.
3.) Needs wear marks (a pile of hulls at your feet is the best method)
4.) Any functioning pump gun (even the chinese, turkish, russian, south american knockoffs) is worth a sub $200 price.
Shooting everything from 7 1/2 junk wally world promo loads to buck shot and slugs should get you and your new gun well acquainted.
For low cost buck and slug loads, I prefer the Winchester Super "X" lines. 15 round boxes at wally world were under 10 bucks 2 years ago so expect $12 or so now.
I feel these are a little cleaner in the barrel than the Remington "Express" line of ammo.