The blow off tube will work well for your primary. But I would not use it for the secondary (clearing). Durring the primary fermentation there is rigorus fermentation action, and therefor the need for the excess gasses to escape. Durring this process, an airlock may not provide a large enough avenue for the gasses to escape, so a blow off tube may be desired.
However, in the clearing stage, the fermentation is all but complete, at least it is not happening at the prior rate. A collection of CO2 at the top of the carboy (or bucket) is desired to help protect against air borne contaminates. I would splurge on the couple of dollars (euro's?, ducketts, ect) to get a quality air lock for the clearing.
Good luck with your brew! What are you planning to brew?
I didn't add enough corn sugar the first time I bottled, so it took me twice to get the theory and practice down. If you don't want to bottle, don't. This is your beer and you should do with it what you like. You could drink it (flat) out of your clearing bucket, and some of us do.
Primary #1:Apricot Amber
Primary #2: Dry Hopped Amber
Secondary #1: Nothing
Bottles: Head Butt Pale Ale, Vanilla Cream Porter, IPA, Wee Heavy Scotch Ale, Aventinus Clone, English Brown
Planning: Peach plambic, Summer Shandy