What kind of opinions are looking for? Like every other caliber on the market, there's gonna be folks that love it and hate it. I don't see a need for one in a revolver. But the rifle is just plain fun.
My opinion is that it is a REALLY sweet youth trainer and super accurate target/plinking/varmint gun. I believe the .223 can be just as good for accuracy and varmint but not really all that great for all around target and plinking, nor is it very good for a youth trainer (too much bang), but it is much cheaper to shoot (I believe) than the 17HMR.
My opinion is that if I wanted a youth trainer, I'd get a .22 just cuz they can be had for a song and shot all day long for less than that. For Varmint, I'd get a .223, though currently I use varmints as targets and conditioning for my deer rifle (.270
)
I ALMOST bought a 17 HMR. I think I have myself talked out of it now though.