I just faced this question about a month ago....
The 110V harbor freight wire feed welder is pretty bad right out of the box. It is an AC welder, not a DC welder (like you need for both MIG and Flux Core, no company sells wire to use for AC flux core welding- it just doesn't exist!). For about $60 you can get a bridge rectifier, a 100,000 uF capacitor and a resistor (to bleed the capacitor down when not in use), and that turns it into a decent DC flux core welder. Then add another $15 for random materials and time to modify everything (heavy gauge wire, proper odd size connectors, etc). You can't, however, do any thin metal, (two selections for power) and it still can't go too thick either (3/16 MAX).
Then you have the ground clamp... it *****. $15 for the tweco style ripoff from harbor freight to replace it (which is an excellent ground clamp!).
So for a little over $200, you have a welder that has only two power settings. It can't do thin metal at all, and it certainly can't do 1/4in or larger. Limited usability for different metal thickness. Only on weldable steel (no fancier metals). It also only has to break once out of the 90 day warranty and you need to buy a new unit (another $120 or so), at which point you are at $320 or so invested for that welder. Some people have good luck with those units and they last 3-4 years, but... then again a lot don't. No MIG capability either. Wire feed can often be inconsistent too. No replacement parts (except for eBay sellers selling parts taken out of broken ones... obviously try at your own risk). The duty cycle is also really low (it may have the same rating as a Hobart Handler 140, but in reality the Hobart is underrated for what it can do). The fan in these HF units should really be upgraded (another $10-15).
The HF welder will also be a hot tip welder (not a cold tip like the Hobart).
Too much to fix with the HF welders. Not worth doing it at all..
For $430 from zoro (with 30% off coupon) you could get a Hoabrt Handler 140. All aluminum drive system (durable!) and 5 heat selection settings. Comes with a good ground clamp (all though still not as nice as the tweco style ripoff one). MIG capability and a 5/3/1 year warranty along with the fact that you will have parts available for many years to come (from both miller and hobart). Can do 24 Gauge steel to 1/4in plate. Steel, Stainless Steel and Aluminum capabilities.
I have a Hobart Handler 140 and love it.
I also got about 40 lbs of flux core wire for $40 on clearance from fastenal, so I've got plenty of wire to learn with!