Pros: Easier than a collapsible steamer; food does not get stuck; easy cleanup
Cons: Too small for large quantities, bulky items; takes up same storage space as another pan.
All-Clad has several steamers that can be used with its pans. I recently reviewed the 12 quart Multi-Pot, which comes with a steamer basket. That product is great for steaming large quantities. All-Clad also makes a large (11" diameter) steamer basket that can be used with its 6 and 8 quart stock pots; I have not tried that one. But when you just want to steam a moderate amount of food -- maybe some vegetables as a side dish -- this 8" diameter steamer is just the right size, and is easier than getting out a larger pan. For me, the convenience of this accessory justifies its $40 price.
This steamer fits All Clad's 3 and 4 quart saucepans. The steamer is designed exactly like the double boiler that fits the 3 and 4 quart pans, except that it has holes in the bottom to allow the steam in. It looks almost like a saucepan itself, with a long stay-cool handle just like other All-Clad pans (and yes, it really does stay cool). It is made of bright shiny stainless steel and matches the rest of All Clad's stainless line. The metal is considerably thinner than on the saucepans themselves, but that is not a problem, because you are not putting this thing directly on the stove, but rather attaching it to the top of saucepan. Epinions does not seem to have a photo, but you can see pictures on the various online merchants.
This steamer insert is very easy to use: put a little water in the bottom of your saucepan, put this insert on top with your food in it, and put the sauce pan's lid on top of the steamer. It makes a tight seal with the saucepan, and steam from the boiling water in the pan rises through the vent holes to cook your food. When the food is done, you use the steamer's long stay-cool handle to lift it off the sauce pan, shake out any excess water, and pour your vegetables onto a serving dish.
I used to use one of those inexpensive, collapsible metal steamers that seem to be available everywhere. It worked, but it was a pain. Since it fit completely inside the sauce pan, it had no external handle. You had to remove it by lifting its center post, which was very hot since it had just been sitting in the steam. Once you managed to get it out of the pan, it was awkward to transfer the food to your serving dish, and bits of food would sometimes get caught in the collapsible leaves of the steamer. This thing is much easier - the stay-cool handle allows you to empty it just like you would a saucepan, and nothing gets caught on the smooth bottom.
The only drawback I see to this steamer is that unlike a collapsible steamer, it takes up the same storage space in your kitchen as another saucepan. But it does have a hole in the handle for hanging, like other pans.
One note of caution: I have heard that the steamer insert, and the double boiler, do not work as well on the "loop" versions of 3 and 4 quart pans -- the ones that have the small helper handle on the front of the pan. Apparently the loop prevents the inserts from seating quite as securely. I do not have any personal experience with that problem, as I use it with a 3 quart non-loop pan, but it is something to investigate if all your pans have loops.