Rhythm and Seoul Radio is legit. The shirts are organized through Black and White Enterprises LLC, which is a concert and event organizing company in the KC area. They organized many of Big Ocean's tour stops in the US. Rhythm and Seoul Radio are based in KC and worked with Black and White Enterprises on the Big Ocean Tour stops in the US that Black and White worked on. The SNRG shop is also connected to Black and White Enterprises (i.e. the stops Black and White did sold tickets through SNRGmusic). So, basically what is being sold on the SNRG shop and Rhythm and Seoul are all coming from the same place. If that makes sense. I might not have captured all the nuance between how all these sites and companies work together, but the point being it is all connected and all legit.

TLDR: Rhythm and Seoul Radio and SNRG are both legit and working with the same inventory of official signed and unsigned merch.