To answer your original question, spools are infinitely more reliable than any other option because they are just one single machined chunk of steel and have no moving parts. Nearly everything else in the axle will break before you take out a spool. Of course, there is always going to be the jackass after me who knows someone whose cousin's brother's step mother's uncle broke a spool. But lets just say that its so rare that it is virtually not even worth considering. Statistically it would be like getting struck by lightening 4 times in the same spot on the same day while also winning the lottery in 7 different states that same day.
But I agree with jrowe ... I wouldn't waste your money on a 9" or a D44.
J. J.