As someone who's got the "Metcal experience" just yesterday, I guess I could weigh in.
I've been a happy Hakko FX-888 user for several years now as a hobbyist, and I can't really say I've noticed much in terms of insufficient thermal response of that iron. I actually like it quite a bit. However, this week I ran across a Metcal MX-500P second hand, in very good shape, for EUR 50. Given the praise for Curie Point technology - and Metcal irons in particular - I've been seeing on this forum over the years, I decided to give it a shot. I paired it with a brand new MX-H1-AV handset + stand (aka MX-UK1) for EUR 130 from E-bay, and some tips.
So I can compare it to my FX-888, even though I realize they're not really in the same class, as e.g. a JBC might be.
It sure is fast indeed. Heats up out of the stand in a few seconds and melts most joints pretty much instantly. I've been desoldering some through-hole boards today, and it was especially noticeable with some solder wick, compared to the Hakko, often wicking up all solder out of a joint in a second or two on touch. Although I already enjoyed working with the FX-888, the Metcal really makes soldering a pleasure as it's so much faster.
I did actually lift two pads with it, which rarely happened to me before. Not sure why yet - I measured my STTC-137 tip at 370C, just a bit higher than the 350C I usually use on the Hakko. Could be the specific board I was soldering, I'll see if it happens to me more often.
From the online pictures of the MX-H1-AV I thought it looked to be really long, which I was slightly concerned about. However when it showed up it turns out it's actually a bit shorter than the FX-888 handset (and thinner), and a shorter hand-to-tip distance as well, which indeed is nice. For the workstand, so far I actually prefer the FX-888's: I think it's slightly easier to reinsert the iron, I like the (grey) sponge better, and the rubber with the brass wool is handy as well. Overall I think it looks a bit better than the bulky Metcal stand.
And yeah, the MX500 hums, even when it's off, as the switch is on the secondary side of the transformer. That's a bit annoying. The 5000/5200 (and perhaps the newer 500?) don't have that issue I think.
So far, really happy with it. :-)