There seem to be many factual errors on flyrockets.com and considering how many people hit that site, corrections would certainly be wise.
Here is one of perhaps 20 or so errors I have seen:
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"Ha! If I have a one pound rocket I can now see the ratio of thrust to the weight of my rocket. The choice is again, fast and brief or slow and long. In general, the safe minimum lift-off weight ratio is 10:1. IE. 10 lbs. Of thrust for every 1 lb. of rocket."The rule of thumb I have been using and teaching for several decades now is 3:1 minimum and 5:1 target for thrust to weight ratio.
10:1 is "very fast".
Jerry