Like a duck to water, surprisingly.
Apparently Gas less is sometimes better than CO2/Argon outdoors as the shielding gas just blows away outside whereas the flux produces the gas right at the point it's needed most.
I had a bad experience with a stick welder a few years ago (I just couldn't do it, couldn't strike and maintain an arc so gave up), flux core in comparison is like child's play. With some research and practice to understand min/max volts/amperage and feed rate, etc. I was able to judge when I needed various settings and what to expect etc.
During my practice week, I had thin sheet metal (old microwave shell) and "infinitely" thick old brake disc to practice with, so got to know from the extremes the properties of thin and thick metal. So I got to practice how to not blow holes through the thin metal, and how to get good penetration

in the thick metal. I was able to test strength by welding the end of a 10mm rod of steel to the disc with a butt joint, then levering it to test its strength. I welded bolts to it and tried hammering them off, they just bent over

... So I got to test welds to failure to figure out when you've got a bad weld with little to no penetration.
I got one spatter drop go through my pants and have a dot on my leg as a result, but it didn't really hurt. If I wear these pants to work again, people are going to think I'm a stoner.

What did hurt was the shard of metal from grinding (I had a face shield on, but somehow something got past it, probably from below) embed itself in my eye on Saturday. I couldn't see anything obvious in my eye, but I could feel it, so I assumed it was just a scratch. Today it wasn't getting any better so I had a proper look in the mirror with my camera zoomed in and saw a dot of metal near my pupil, so went to the eye hospital after my attempts to flick it off with the corner of a credit card failed as I couldn't get near it without girling out. They numbed it and got it out. I'll invest in a better face shield in future!
I've little to compare the welder to, but I've already fixed a few things, and also bought 2 new rolls of flux core which turned out to be very low on flux. I assumed they'd be an upgrade to the stuff that came with it, but instead it was nasty and horrible to use (yes it was definitely "flux core", not regular mig wire). It left no residue, unlike the stuff that came with the welder leaves a white powder you brush off, evidence of the flux. I put the original stuff back in which is much nicer. So money well wasted as I got to experience the difference between different qualities of wire.
I'll update my original thread with pictures, etc shortly. I spent 6 hours this evening refitting the subframe, shocks, brakes, prop shaft, arch liners, sensors and exhaust, then went for a 20 mile
blast test. The tracking should in theory be out because I've had the arms off and didn't record the position of the adjusting cam-washers, but it feels totally normal. I'll get it tracked, but right now, the car is totally fixed. So I've very pleased. It in total cost less than a new 2nd hand subframe and I've now got a welder and new skills out of the other end.
What's your welding experience?