Rocket stove materials (cooking stove, not mass heater)

With kids out of school tomorrow, I'm considering a practical family project that involves playing with fire - a back patio rocket stove. I'm interested in learning from your experiences before I begin making my own mistakes. I did read this excellent thread.

Approaches I'm considering:

Brick stacking. Example https://www.youtube.com/watch?t=1&v=fz2ssyGfg58]here.

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Concrete block. Examples here and here.

Nested tin cans. Example here But I probably won't take this approach, for reasons described in the thread linked above.

Cast concrete in 5 gallon bucket. Example here: here.

Cast in 5 gallon bucket, but use cob instead of concrete. (No examples, haven't seen anyone doing it.)

Molded from cob, ie no bucket, but like the 5 gallon bucket approach I'd still using a pipe to form the burn chamber

Goals:

Involve and interest my kids (11, 13, 17). Prefer fast gratification - start project in the morning, cook on it same day.

Effective. If this experiment works, we'll cook on it often.

Inexpensive enough to recycle and experiment again until we love it.

Enjoy learning. Enjoy working with our hands together.

Any suggestions what to try, what to skip, and what I'm not thinking about yet that I should consider?

Barring other input, we may make one fast from brick or block to cook breakfast on, then see if we can mold something from cob that works better. (Better = burn super clean, cook well, minimum fuel use.)

Based on the instant gratification caveat, I would say the block stove is the option to go with. I've seen a two burner one put together in minutes.