Where I bought it: a Cubewerkz locker (does this actually matter)
When: a few days ago
Thoughts:
Oh boy. The out-of-the-box experience was not stellar (pun intended) and I honestly didn't like this puzzle very much at all. I did try a nonmagnetic Galaxy v2 briefly at my last comp and my initial impressions of that was about the same: this puzzle is very sluggish compared to my Galaxy v1 (which isn't even lubed), and it's tiny in comparison. It's also significantly lighter at about two-thirds the weight, but apparently my arms are incapable of distinguishing weight differences below 500 gf; this probably makes more of a difference when doing loads of solves.
The good: Firstly, reverse corner cutting. On the v1, if you tried to reverse cut more than about 16°, the whole layer deforms and it locks up; on the v2 M, reverse cutting still isn't "effortless" per se, but it's significantly better and the deform-then-lockup problem is much rarer. (Effortless reverse corner cutting is a meme and doesn't exist on any puzzle anyway.) Secondly, the presence of magnets makes accidental turning of faces harder and obviously helps with layer alignment.
The bad: OOTB experience, like I said above. It definitely needs to be loosened slightly and maybe broken in; I did a quarter turn on each of the twelve faces and that seems to help somewhat. Maybe wiping out the factory lube helps too. Also, it's significantly pricier than both the nonmagnetic v2 and the v1.
The neither-good-nor-bad: The size takes some time to get used to if you've been using the v1. The magnetic pull on each turn is pretty noticeable, giving the puzzle a bumpy feeling. The Galaxy v1 is very fast and smooth, but the v2 M seems to trade off that speed for stability. No idea if fast lubes will change this because I don't have any on hand right now.
Something to take note of if you want a non-standard colour scheme: The Galaxy v2 (and v2 M, obviously) have two different types of edge parts; if you want to switch two faces that have different M:F ratios, you might need to disassemble other faces and swap those pieces as well. The sculpture version comes with 5 black M edge parts and 5 black F edge parts (and 5 black corner parts, obviously), so switching in a black face shouldn't require further disassembly.
I've done about 40 solves on the v2 M, interleaved with some solves on the v1, and overall it looks like I'm just slightly faster with the v2 M. It's not an "instant main" like some people make it out to be, since the v1 was already a very good megaminx, but the data seems to point to it being a (slight) upgrade. (But also consider the fact that I don't know how to set up cubes; maybe it becomes even more amazing if you're good at that.)
Update (2018-05-17): I've sunk probably a few hundred solves into it at this point, and I'm seeing clearly better times on it than on the v1 (1:30-ish versus 1:36-ish). Definitely main material now.