I have one, and yes it works very well, I would say it's worth getting, but there are a few downsides to it, one is the cost, I spent around $400+ on my MiSTer FPGA
here was the cost break down:
$61 ---- Mister FPGA IO Board v6.1 XL
$64 ---- Mister FPGA SD Board XSD v2.5 128MB -- Memory
$51 ---- MiSTer FPGA 7 Port USB HUB V2.1
$80 ---- MiSTer MT32-Pi Package -- MIDI sound
$135 ----DE10-NANO CYCLONE V -- back when it was cheap
and then about $100 in parts for a custom case.
Another downside to the MiSTer FPGA is that it is very fragile, the ports and connectors on the DE10 Nano can very easily break right off with little to no force, the DE10 Nano was not made to be a consumer product, and is not a durable has a cell phone or something like that, I would say it's slightly less durable than a raspberry pi, so I spent that extra $100 or so on a case for it that extends the ports out to plugs on the outside of case that can be easily replaced if damage happens.
The other downside is that the ao486 is kinda slow, you are not going to play Quake with this, and Duke Nukem 3D is also too slow, it will play other older games just fine however, and I have Windows 3.1 running on it, it runs kinda like a fast 486SX, basically no math co-processor.
The retro game systems seem to run perfect, or at least every game I have tried, however and here is the last downside, most of retro game systems running on the MiSTer FPGA don't have "save states" or "cheats" like you would have on a emulator that runs on a PC, so when you play a game that you want to beat you basically have to pause it and leave it running until you are ready to finish it, and yea I am just not doing that.