I ordered a couple yesterday. With FPGA Tech you won't have any lag. Emulators have lag. I have been using Emulators since I played C64 games on my Amiga back in the day. I Love Emulators.
With Dedicated FPGA based retro consoles, you put the disk or cart in the machine and Boom, you are playing your Nintendo, (or whatever system), games on your modern TV with Full HDMI support. Using and upscaler can covert a Composite, (or whatever), signal to HDMI, but it has lower picture quality and also introdues lag. (My Favorite Upscalers are the RetroTINK brand. They have very low lag).
The FPGA based systems from Analogue and Polymega are some of the best out there. Much better than an Emulator. (Once again I love emulators).