Never tried the U-pol line just because I have had such good luck with Evercoat products, they also have very good tech support and their Rage body filler line is great. My buddy that built bodies taught me the Evercoat polyester primer trick years ago and I have used it ever since. The other thing he taught me I have had good luck with is after your done with your polyester products shoot a coat of epoxy primer on top before your paints sealer (block out to 600-800 grit) , couple reasons it provides a barrier against bleed through of any accidental reaction to the catalyst for filler and two its hard and tough and holds the soft polyester together, and on metal bodies it is waterproof. The other great product that is cheap I know of and used between coats of primer & paint ( don't use solvent based wax & grease remover, use it only on bare products) Is Sprayway glass cleaner for in between coats of primer & paint, found the tip on a airbrush site, its cheap available most every town and is a aeresol, works wonderfull. Best of luck Matthyj