I think they sound like a great idea but I did not bother with my dog in the end. I only very occasionally think: "Wish I had crate trained her". I very often think "Wish I had trained my old dog" though. It would have helped her anxiety heaps to have her own den.
But Banjo is totally bomb proof. She also doesn't really mind being tied up - just lies down and relaxes.
Camping is one place where I would have used it if I had one though. The first couple of nights we camp Banjo keeps darting out of the tent to chase the nocturnal wildlife - real or imagined. It is very annoying and I also don't want her to harm some rare bandicoot...
But in the end my cost/benefit analysis swung towards the nay. Don't listen to me though because I have never tried them!