Barry, "Black Flash"or No-Glow High Output Covert IR image quality is, in my opinion, equal to both Lo-Glow Semi-Covert IR and Standard IR but the more covert cams will cost you more.
Although, I have only used "Black Flash/No Glow" game cams by Reconyx, I'm sure the better name brands produce a product, as far as image quality goes, at least equal to their less covert models.
BUT, again in my opinion, spending more on a completely covert cam isn't necessary for capturing game on film, semi covert is sufficient.
HC