I bought this to use with my Nintendo 64 on my 4k TV.
First issue was no picture. Solved after the scanning HDMI port. Next issue was a blue screen with no clarity why. The reason was because it was working but no picture was coming through because the Nintendo 64 wasn't displaying anything.
After a couple attempts to clean the cartridge I got sound and a picture.
One thing that did surprise me about this is that the external power supply was not actually necessary to use. While the picture did look more crisp when using it, it did somewhat look worse because of the jump to 4K. Running it without additional power has been alright so far.
Used it for around 12 hours so far without any noticeable problems.
1 star off because of a lack of info on how to get this running properly. I got lucky and reddit posts in the past years about blue screens saved me from returning this prematurely.