I've been using backpacks in my commercial cleaning business for about
16 years. They almost never break down as there are no moving parts
except for the motor. We're still using the oldest one but had to
replace the motor once. On some types of carpet (mostly cut pile) they
don't work real well and in one account we successfully use a turbo
head attachment. The only ones I've ever purchased are the Pro-Team
vacs. Pro-Team was the originator of the backpack (to my knowledge)
and are pretty much the standard in the commercial cleaning industry.
They are kind of pricey for home use, about $400.