speaking from experience here, the ones in my run about sierra have been in several of my sierra's and were bought from PE about 8 years ago, so they do last well

the downside though (as i might find to my cost) is that ford don't recommend them
probably because they don't make any money on the little crappy versions they sell every 3 months
tca failed after 4 months and ford won't do a warranty claim on it because "you've fitted poly bushes"

angry letters are flying at the moment but as a whole, this is the first ime i've seen this problem occour

lots of people are split as to who to get them from as well, but (again) in my personal experience you get what you pay for
20 minutes a side with the PE ones from wheel off to wheel on, in the garden, inners and outers at the front (but i did cheat and use an air compressor to wind the nuts and bolts in and out )

for the rears the beam bushes have mixed reviews
some sa it make the ride rock hard and other (me again) have found that it's more likely that the old bushes are so knackered that you feel the new ones are ultra stiff in comaprison

rear trailing arms need the beam out to make life easy

HTH