Claim #1 (detractors): Knockouts are not real roses. Only DNA can answer this question. Rice, soybean, and grape genomes have been sequenced, but there are no published genomic comparisons of knockout versus classic roses. But, considering his parents, Razz must be as REAL as Mr. Lincoln. Both are hybrids of the genus Rosa--Razz a shrub rose and Mr. L a hybrid tea. And Googling indicates Razz was created by the respected Wisconsin rose breeder William Radler, who hybridized it from fungus-resistant Carefree Beauty seed and pollen of the floribunda Razzle Dazzle. So, until the rose genome project proves otherwise, I judge Razz a rose.
Claim #2 (fans): Knockout roses require zero care. Mr. Radler bred Razz for people who prefer TV to gardening. My plant factsheet says Radrazz “shows great hardiness and disease resistance”. Nonetheless, in spring my plant's leaves looked like someone had taken a paper-punch to them—a situation remedied by insecticide that cost more than Razz did.
Also knockouts are as susceptible as any rose to a very deadly disease called Rose Rosette. It's caused by a microorganism carried by mites and is manifested by brushy "witches broom"-type growth. Infected plants die--nothing cures them—and must be destroyed before they infect Rosa cousins. Bottom line: Razz is mortal.
Claim #3 (fans): Knockout roses are self-cleaning. In plant lingo, “self-cleaning” means that plants jettison dead blooms and pop out fresh ones without your help. But take this with a grain of salt! By July Razz was a sea of dead blooms and was cleaning himself very slowly. So I took notes at a local nursery when they instructed folks on how to snip dead blooms (the cognoscienti call this "dead-heading") to keep neighbors drooling.
To see if this was worthwhile, I enlisted my sister, who has 12 knockouts, for an experiment. She “dead-headed” 8 plants and let the other 4 "self-clean". An "impartial observer" then rated bloom performance and found Self-cleaner Control versus "Dead-head" Experimental plants indistinguishable from the curb! So, yes, these plants are somewhat "self-cleaning" and don't waste your weekend helping them.
Claim #4 (detractors): Knock-out roses cannot substitute for the real thing. Scientists eschew "anecdotal evidence", which is as it should be when it comes to medical research. But today I worked as a go-fer at the Nashville Rose Society, and just look at this trio of winners! Based on this anecdote, I'm with the detractors.