ESL is a short for "Electron Stimulated Luminescence".
Acording to the article in Wikipedia (Although Wikipedia writ??? that the article about Electron Stimulated Luminescence is written like an ad), ESL lamps operates similar to a CRT, but but lacks magnetic or electrostatic deflection.
Electrons from a cathode, passes through a vaccum atmosphere and strikes a phosphor coating, causing it to glow.
Because this mothed is very reliable, the lamp should have very long life. However, since the electronic driver integrated inside the lamp, the lamp life depends on the driver life which is at max several years if well made.
So like LED light bulb and sometimes also CFLs, the general failure mechanism of ESL lamps is "Ballast electronic", provided that an ESL lamp that operates with an external driver will be made, so when the driver will fail, it will be seperately replaced and the bulb continue to operate with the new driver.
The CRI of ESL lamp, like fluorescnets and induction, depends on the phosphor coating. Vu1 ESL lamp have a triphosphors coating and hence they have Ra8=85, similar to most CFLs.
Also the dimming possibility of ESL lamps, like CFLs and LED lightbulbs, depends if the driver optimised for working with a dimmer switch. Vu1 ESL lamps are dimmable in this case.
The ESL lamp is for sure mercury free, as the lamp uses electrons through a vaccum to operate the phosphors like a CRT tube, instead of UV radiation which the mercury is the only element that produce them efficiently.