I was lucky enough to be given my Instyler second hand a few years back to help with using less heat on my (at the time) severely damaged hair.
I have thick-ish / frizzy / wavy / dry / blonde hair down to my bra strap (my profile pic only shows the layered hair at the front the rest is behind my head.) I find this works really well for my hair type at smoothing the frizz and styling perfectly. It did nothing for my mother-in-law who has short fine hair, so I think this really depends on your hair type how well the Instyler works for you.
I only ever use the Instyler to curl my hair, not to straighten it (I use GHD for that), I just love the results I get with minimal effort - which is pretty much the same amount of time it would take me to straighten it. The curls are loose and glamourous, fall nicely and don't 'drop' out during the day and/or night.
The Instyler has 3 heat settings which I find handy. This is displayed by 3 little lights and once they stop flashing (maybe 1 or 2 minutes) you are good to 'roll'.
Its easy to hold and twist as Im curling and you can get right to the back of your hair. It is a little on the noisy side but that personally doesn't bother me. The comb part has lasted really well and the roller looks just like new even though I've thrashed it over the last 4+ years, more so in the last year. I've dropped it numerous times off the bathroom vanity and its never broken...which astounds me cause its taken some hard knocks. So if it was to conk out on me tomorrow I would feel its had a very good innings! If I was to say one bad thing about it, it would be that sometimes it can be a little difficult to stand up while waiting for it to warm up but the swivel cord helps to move to balance it.
It did take me awhile to get the hang of using it, so like anything practice is key, now I couldn't see myself without one. If this one ever stops working I really hope I can get my hands on another one. Maybe I should keep an eye out to keep a back up... hehe
I wish I made my hair soft and amazing like in the adds but nope! I wish I had bought a ghd.. This one isn't great, dsnt donit any better than an ordernerry brand. Oh and it is loud!