Richard is correct, the higher end Rinehart targets are made entirely of the same material as the core of the woodland buck and hold up much better. If you don't mind a target on the smaller side, the Rinehart Broadhead Buck is a much better target than the woodland buck and takes the same insert. Sometimes you can even find a factory blemished broadhead buck.
Also, I haven't owned them long enough yet to determine if they get brittle but most of the targets on my backyard course are made by R&W targets and I am extremely happy with them. They are an excellent alternative to the big 2...especially for stickbows as the arrows can be difficult to pull if shot from a bow with training wheels.