I had found this thread after getting a GT120 myself.
As an user of other Curie-point induction irons (MX500P, MX5200, Thermaltronics TMT-9000S) the GT120 is a bit disappointing for the price. You don't see the iron heat up as fast as the curie-point irons, and heat delivery/recovery is noticeably worse. I'm testing with a chisel tip on both so fairly "fair" I think. This *is* with the heater core + extra tip on the GT120 (it ships with a heater core) rather than the all-in-one heater+tip. The two-piece construction was supposed to let us have much cheaper tips I presume, so part of what interested me in the GT120.
It's still a nice iron & works well. But if you're coming from the other Metcal units (or trying to get their performance) you'll be disappointed. I don't have any of the other lower-frequency Metcal units so I'm not sure if this performance is related to the fact it seems to be a 450khz drive, whereas my other units are the 13.56Mhz drive, or it's related to the slightly slower measuring loop as it has the 2-piece tip construction on the one I tested (along with RTD response time).
Like most Metcal stuff the soldering stand, wand, build quality, etc are all very good. So you aren't paying the premium for "nothing" and in terms of overall quality it seems to be in line with Metcal expectations for me. But if you have heard of the nice Metcal performance due to their Curie-point induction heaters (aka 'SmartHeat' name they use), be aware this iron isn't at the same level.
On the huge power brick - it's actually an off the shelf Meanwell unit (P/N is GSM120A48-R7B, can find on digikey etc). So replacement won't be too hard if you ever needed it, and it means there is no smarts in the power brick, it's just 24V 48V out. One possible nice thing here is you could use the iron mobile, as it just needs any 48V DC source. It also means the provided power brick is universal input voltage, just swap the power cord end if you want to convert to another country, no opening the unit like the MX500.
Hope this is helpful to someone else looking at this!
EDIT - I was wrong on P/N of brick, was going from memory. It's 48V out once I checked in lab, edited post to add right voltage & PN.