I'm very familiar with that bike - my dad owns the men's model in a different year. It weighs about 33-34 pounds, and it's no slowpoke - I've timed myself on my commutes with it, and it was surprisingly close to my fastest ever. Plus I felt it was comfortable to boot.
The quality of parts are OK. I wasn't crazy about the rear derailer claw, but I was able to tune it so all the shifting worked perfectly with the thumb shifters on my dad's version. (I guess some versions have twist shifters?) The wheel hubs were a lower quality assembly (retainer rings with fewer ball bearings) but spun great once I overhauled them. The most important thing is that it's not heavy as a tank, and it will have strong braking if set up properly. Overall the assembly and adjustment had major room for improvement, but it's all fixable. Even if you don't touch anything, I doubt it's set up worse than your Huffy.
If the bike is in good condition, and you enjoy riding it, then I would not think twice about a $20 trade-in. I suspect he's giving you an unusually good discount because he likes you, and if it were me, I'd jump on the offer. It is a major step up from your current ride, and even if you don't stick with it, it has value as a backup bike or a loaner bike to a friend. If nothing else, it has more resale value than your Huffy.
The front wheel (only) is a quick release, so if you haven't worked with those before, I suggest you ask the bike shop guy how to attach and detach the wheel properly - the quick release doesn't work like a wingnut. While you're at it, ask him to show you how to quick-release and reconnect the brakes (center-pull cantilevers) in case you get a flat tire. The quick release front wheel is easily stolen if you live in an area with any crime at all, so lock it and/or add deterrant with a $1 hose clamp from the hardware store. (Clamp the quick release lever to the fork so a potential thief at least needs a screwdriver and some time. If you don't want the hose clamp to scratch the paint, wrap some electrical tape underneath the fork where the clamp will be attaching.)
The bike's innertubes uses Presta valves, so make sure you know how to use those and have a way to top off the air in the tires. (If you don't have a Presta-compatible pump, there is a converter for the usual car-style valve and Presta valves that the bike shop can sell you for a buck or two.)