You haven’t given us many details to work off of. What does ROK Diagnostics do? Who is their target market? Etc., etc. I’ll share my thoughts since I don’t think they’ll change even if details are supplied.
To my eye, the symbol / monogram is dated looking and tough to read. Without the ROK type, I would not have looked at the monogram and come up with ROK. Maybe Rr, Rs or Rk, but definitely not ROK. The font or lettering you’re using for the symbol reminds me of a stereotypical heavy metal band from the 80s. Think “This Is Spinal Tap.”
Option 1 – The Two faces being used don’t mesh together particularly well, the kerning and leading need work, and the type is too close to the symbol.
Option 2 & 3 – To some degree, you’ve improved things, but that’s not saying this is ready to go. The proportion of the type to the symbol is off, the face is not working with the symbol, the kerning and leading both need work, and the ring around the symbol is too heavy.
On the positive side, I’d give you points for using one color and coming up with a logo that would work across a variety of mediums. Though that thin space between the R and K could be an issue.