The first time I used it, I was afraid to put too much heat under it. So I set the temperature at slightly more than medium, and waited as it took *forever* to start boiling. It did boil though, and without trouble too. It's very relaxing watching the water start to swirl around through the pot, heating and bubbling gradually. This kettle can take flame too, and I think it would be lovely to watch it on a gas stovetop.
The second time I used it, I started a bit higher, and had moved up the temperature almost all the way to high by the time I was done, to get the water boiling sooner. I figured the worst that would happen is glass shards and hot water everywhere...I still have my SS kettle in case. But nothing happened, and all was well.
I do notice that you can't fill it all the way - it needs some air in the top to get to a full boil, for some reason, and if it does start boiling hard, the water and steam tend to shoot out of the spout quite jerkily, which could be dangerous. But even filled just three quarters full, it still makes plenty of water to fill a nice sized teapot, and when it gets dirty, I just stick it right in the dishwasher, and it comes out nice and clean. My SS kettle has hard water stains that I've not been able to scrub out...not a problem with the glass kettle in the dishwasher. I've also noticed a difference in water quality...perhaps the SS was contributing more of a metallic taste to the water than I had noticed previously.
It's a bit spendy at $29...and definately a "luxury" item, but I do really like the way it doesn't take up so much space on my stove, and is so easily cleaned that I don't have to look at a constantly dirty kettle on the stovetop.
One downside though - I have to keep the stovetop cleaner, because you can see right through the kettle to whatever is behind (and under) it! That's not necessarily a bad thing though...
Anyways, if you're wanting something pretty, dainty, and still very functional & easy to clean for your stove, splurge on one of these kettles. You won't be disappointed, and there's the added bonus of no metallic taste added to the tea water (if you currently have a metal kettle).