I think half the fun of canoe building is completing a successful steam bending operation. Of course half the frustration of canoe building is a failed steam bending operation. I do have one of Lee Valley's bending straps and it works great. Its very effective but it really is almost a two or three man operation to hold the handles and another person to loosen the pressure on the wood. I have used it when I'm doing steam bending classes to see how tight of a curve I can make with it and have gotten down to a 4" diameter circle with 3/4" square stem stock. The one in the picture was a 6" diameter, but over the years it has opened up a bit. There was so much pressure on the strap it took two people on each handle to do the bending and another person operating the ratchet to loosen the pressure.
In the shop, for almost all the canoe bending needs, all I use is a 1/8" steel strap that has a hook bent at one end. The hook acts as a stop for one end of the rail or stem. At the other end of the stem or about 6 ft down the rail, I clamp the steel band to the stem or rail. using a pad of wood to protect the rail or stem. This system acts like a poor mans Lee Valley strap. The bent hook prevents one end of the wood from slipping. If the wood can not move in the strap, as it is bent, it puts the wood in a great deal of compression and the wood will buckle on the inside of the curve. Fortunately almost all the time the clamp will slip just a bit even when its really really tight. This slipping will release a bit of the compression but if it slips too much then the outside surface of the wood will be in too much tension and the face of the wood will split which is the most common failure that occurs in steam bending.
The nature of all woods is that it can be compressed much more than it can be stretched or put in tension.
When bending a tight curve such as on the Molitor there is as much as a inch of difference between the length of the inside surfaceof the stem and the length of the outside surface of the stem. The inside of the stem will try to compress 1/2" and the outside will try to stretch 1/2". The outside can not stretch that much so the face of the stem will split. By securing the stem to a steel strap so that the wood can not move, when the unit is bent, the wood can not stretch because of the stops on the steel band. The more the unit is bent the more the wood is compressed, until the inside surface of the wood fails and the inside buckles. Before that happens, if a bit of pressure is released from one of the stops, the wood can stretch a bit , the inside compression is relived just a bit and the outside surface is put into a bit more tension.
For strap material, thin sheet metal will work just as good as the heavy steel, its just harder to install stops, clamps slide off and the bent hook system doesn't work. When I need a wide strap such as for a 5" wide coaming which is fairly thin, I cut out what I need from a roll of aluminum flashing stock. For more serious bends such as for a 3" wide Morris stem, I'll use a 1/8 wide steel strap that is 4" wide.