I have a MK4. I elected to get the kit for $850 and build it myself, I'm an electronics technician so it was pretty easy to justify getting it as I knew I could build it.
I built the Lack enclosure for mine and have had great success with it. I've also added a different buffer for my MMU3 along with a Nevermore filter as the latest additions for my enclosure.
It definitely takes up more space than the normal enclosure, but I'm very happy with it. I'd recommend the lack enclosure just because cost savings is so worth it.