I bought a dozen of these (from elsewhere) to replace standard MR16 halogens hung from the usual kind of transformer track lighting. One after one, they started to fail within weeks. I now know why. Don't be misled by all that 'straight swap-out for existing bulbs' stuff. Unless you are 100% sure that you have a voltage-regulated transformer, beware.
After mine started failing, I put a meter across my so-called 12v conductors with no bulbs connected. 15.8v !! No wonder the LED versions were 'aged prematurely'.
This is because an unregulated transformer is designed to push out 12v when given a normal load (say 4x20w). As soon as you decrease the load down to silly amounts like 5 watts in total, up goes the voltage!