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.
The lack enclosure is a DIY enclosure that Prusa wrote an instructable on how to make. You use two IKEA Lack tables to create the frame and then print some parts to hold it all together with some acrylic panels to help keep the heat in. I think my total cost of materials was like $180-$230 for the whole setup. The price includes the filament used to print the printed parts. (I’d upload a picture, but I keep getting errors when I try to share my setup here).
For me the $850 was worth it. Especially because we use Prusa printers for our print farm at work, we even just got the Prusa XL.
They’re definitely a lot more expensive, but the fact that everything is open source is highly valuable to me. They’re also like the Toyota of the 3D printer world (or old Toyota, the reliable kind), they’re just absolute workhorses that tend to not give you too many issues. For me, I wanted to spend my time printing, not tinkering with the printer trying to get it to work.
The kit was worth it for me, but be prepared to set aside an entire day building it when it shows up, maybe even longer if you’re not technically savvy.