I have changed one before. They are not too awkward to change but mechanics do not seem to like them at all (I guess it is the labour involved that they do not appreciate).
FWIW, I would not touch an 'ebay special' or any pattern top arm. My car (if the receipts are to be believed (the nuts seemed new as did the arm when I bought the car)) has failed the MOT today on a knackered arm which was only changed a year ago this month, and it has covered 18,000 miles in that time.
TBH I thought it was the arm that I changed (it was Vetech arm from GSF), although I am told that arm was fine. This time around I have gone for a Lemforder arm from ECP (who incidentally are doing a 30% discount for the winter on oils and suspension parts).
Yes they are cheap, but IME on previous suspension is one area where if you buy cheap, you buy twice (although it appears even I forget that lesson).
If they go again (although at least time I should have good quality balljoints (or at least on one side only this time)) I plan to fit the Superflex upper arm bush kit. Previously their bushes have really impressed me in many aspects (fit, longevity (even over Powerflex) and performance (I.E: your fillings do not get rattled out).
SuperFlex: Advanced polyurethane suspension bushes