I would agree that the ladder/tubing is the most useful component, but they are not very effective. I would opt for spending $20 on a powerhead for a co2 diffuser. These are much more effective because they are "active" and not "passive", like the ladder. I lost links to good, simple DIY active diffusers, but usually they involve bubbling the co2 into some kinda chamber, and having the powerhead blow the bubbles around until they dissolve 100%. I switched to this and co2 levels are through the roof on my 29g!
All said: invest in DIY rather than buying the Hagen system!