I work on all Polaris models, and have so for 18 years.
I will be brief:
models 180 & 280 (2 wheel drive with a transfer wheel)
Well made units with the oldest "drive" system. the bearings wear out quickly causing the front and single side wheels to loose their camber, or become "wobbley". this then leads to the wheel gears to get chewed up and broken.
SOLUTION: replace all 8 bearings on these units every 2-3 years.
model 380 (3 wheel drive WITHOUT a transfer wheel)
As this unit is made now (2010), all previous problems have been fixed. Water management is now glued, belts last as long as 6 years. filter screen has been changed to an inline, larger unit.
the 380 will get arond the pool much faster than the 180 or 280, however, its' "throat" is not as big as the 280 so it will not pick up the neighbors cat as the 280 will.
model 3900 (3 wheel drive WITHOUT a transfer wheel)
This model is designed after the 380, 480, and 280. the bag and "throat" are from the 280 & 480 model. everything else is an advanced heavy duty 380 model.
the 3900 has a bigger bag, better traction with the bigger wheels, hard plumbed water management, and a stainless steel chain drive system.
The entire unit is now UV protected.
***Polaris has fixed the wheel issue last year, if you have this problem, take it in to a Polaris repair center, usually at your pool store you bought it from, and it will be repaired for free.
And finally- please note this on all Polaris 180, 280, 380, & 3900 models:
THE BACK UP VALVE CAN AND WILL CRACK CAUSING ALL UNITS TO ACT SLUGGISH.
Look closely around the jet on the back up valve, if there is a crack OR the black O-ring seal around the jet is comprimised - replace it!!
Make sure a hose float is always placed just behind the back up valve, this will help to keep the valve body off the bottom of the pool and keep it from cracking and it will protect the seal.
feel free to contact me directly if you have questions about your Polaris model.
I will not answer on the Legend models other than to get rid of it and get a Polaris!!